When you look for someone to work on your house look for someone who has experience working on old houses.
OLD houses are built much differently than new ones and it's a totally different set of mind skills needed to do the job correctly.
Given that you are in Boston you shouldn't have too much trouble finding someone who is good with old houses.
Are you going to have to do other work on your old house, like electrical or plumbing? If so I'd do that first.

Thanks, Carol. The electrical was updated about 25 years ago when we bought the house, and plumbing is good. But you remind that I should double check that. Yes, most houses in my area are at least 75 - 100 years old, so I expect a local company will have that knowledge base.

You might want go to the historic homeworks forum and browse, or even contact the forum owner, John Leeke. He's in ME and does consultations for old house projects. Since he may be close to you, that might be useful.

Of course, one of your options is not insulating, either none at all or just doing some insulation in the highest ceiling. For instance just doing the space above the second floor ceiling and under the attic flooring, along with a very good job of sealing air infiltration into the heated space. Installing in-wall insulation is always hard on old houses because of cavity obstructions, access (either exterior or interior wall clading needs to be removed), technical consequences regarding vapor planes, etc. Plus there are some (and I am one) who are not convinced that wall insulation (at least as most people today think of it) is actually good for an old house's long-term survival. It is a modern technology that is somewhat at odds with the technology that has sustained these old timber-framed buildings so well, for so long.

While I recognize the benefits of improving energy efficiency, limiting yourself to attic floor insulation, air infiltration control, and superior penetration -both door and window - weatherstripping will make an immediate, big difference on energy use and cost, without the potentially long term cost to the building. Depending on how you heat, it might also make sense to consider adding some renewable energy capacity to achieve more savings and efficiency rather than just focusing on trying to keep all the heat in.

Lest you think that I am merely talking through my hat from a milder climate than yours, I should point out that I'm actually in northern NY, with a more severe winter than yours. My house is probably a dozen or so years younger than yours, with its original, intact, interior and exterior surfaces. I initially thought we'd have to remove one or the other, but fortunately I put the decision off long enough to have progressed beyond the conventional wisdom to a more nuanced view of how my building works, as opposed to how more modern ones do. We heat with wood (mostly from our own woodlot), and are planning to add significant solar thermal and PV components this year, so we are trying to improve the energy profile that way instead filling the walls with insulation.

Something you might want to explore before you commit to this decision is what is actually in your walls and what kind of bracing you have. Info about this will help you decide whether some of the sprayed-in/blown-in type products would even work in your building. The average contractor really has no idea how to handle old houses, so you really need to talk to an old house expert. (When I go to Home Show exhibitions, I am often shocked at how glib and uninformed the retro-fit insulation guys often are about how to work with truly old buildings, especially the spray-in/blow-in companies. Their experience and notions of old are really more about houses built after, say, 1930.)

If you haven't already done so, you can make a big difference with tightening up the house with caulk and weatherstripping and buy yourself more time to get fully up to speed on this topic.

The quest for environmental and energy efficiency has to be balanced by the net environmental gain realized by protecting and preserving existing structures for many more years.

Here is a link that might be useful: John Leeke's forum, very useful for old house owners

You may want to check with your utility company to see if they're offering any "energy audits" and incentives. They can come in and generally best recommend what to do.

We're just north of Boston, and a year or two there was a "call for your free energy audit" in one of our monthly bills (from National Grid.) They sent a company out who inspected, poked, & prodded. They told us what needed to be done, then told us that N'Grd would pay 75% of it as part of this promo program. They chaulked/foamed all the gaps from attic to basement, installed rubber gaskets around exterior doors, foam pads inside electrical boxes, replaced every bulb in the house with a florescent, and laid down and extra 8" of blown cellulose in the attic, all for about $400.

To get a head start on a contractor, I'd suggest reading the attached from the National Trust for Historic Preservation on insulating old houses.

I've been an old home owner for about 12 years now and we've only and always focused our insulating attention and $$ on the attic and weather stripping our original wooden windows, doors, electrical outlets and fixtures on outer walls. We've also used denim insulation and love love love it - no itching!

I also agree with ultimately working with a contractor who really knows old homes.

Here is a link that might be useful: Natl Trust insulation

Stopping up the leaks will give a large return, sometimes more than insulation.

For old houses blown in cellulose is often the least damaging to install, and does not create moisture issues like fiberglass can.

Attics should always be the first thing insulated.

If you think the R-value of an uninsulated wall structure is poor, think about a roof.
A thin layer of wood with shingles, and then just a ceiling below.

Even a frame wall has outside sheathing of some type, and an interior wall.

The stud cavity is large enough for convection flow to occur in, but if there is a lot of stopping in the walls it is reduced in height.

I second everything Liriodendrdon said.

My house has had blown rock wool in the walls and attic floor since the late 40's or early 50's (the installer's nameplate still has a 3 digit phone #) and with no bad effects to the envelope's moisture-handling characteristics. This is the biggest concern with adding insulation to a house with old finishes inside and out; how will the moisture be able to move in both directions seasonally? If the wrong insulation material is chosen the resulting moisture problems can be very deleterious.
Rockwool worked well here in WV, where we can have really cold, snowy or damp winters, depending, and blistering hot humid summers. Blown rockwool apparently can be the best of all the blown-in types; either fiberglass or cellulose have worse compaction problems that result in loss of coverage at the tops of wall cavities(from what I've heard).
Casey

"Blown rockwool apparently can be the best of all the blown-in types; either fiberglass or cellulose have worse compaction problems that result in loss of coverage at the tops of wall cavities(from what I've heard). "

The problem with fiberglass and rockwool is they do not absorb or release any moisture.

If the freeze line ends up inside the insulation frost can for and then may melt rapidly enough to form water (as opposed ti sublimating directly back to vapor).

Cellulose insulation absorbs moisture as a gas, and can hold it and release it back as a gas more reliably.

A lot depends on the actual construction of the house, the moisture permeability of the interior walls and the siding present.

Water vapor will get into the insulation.
How it then behaves is important.

Thanks for all of your helpful comments. I have an appointment with a contractor tomorrow morning, so will have a few good questions. As a result of feedback here, I am now certainly questioning whether or not we should do this, and upset the integrety of the old house. Maybe we should get an infrared energy audit first. I've read that the City of Boston is arranging those.

I've posted this before, but here goes again. The only insulation we have in the old part of our house is in the attic. We have storms on our windows and have sealed up leaks. We are very happy with this, both from a comfort and heat/AC perspective. Our utility bills are quite reasonable. We are in Colorado. I would not consider putting insulation in the walls; we just don't need it.
Diane

You've received lots of good advice from many different people, especially in regard to the wall insulation question. (My vote would go with the do not insulate people. There are far too many moisture and settling issues to make this a worthwhile investment,IMHO.)

A friend who has many many years of experience in old house restoration always advocates this order of priorities:1)air sealing with caulk, weather stripping, etc. 2)attic insulation 3)basement insulation 4)high quality exterior storm windows and maybe interior storm windows especially on the north side.

Avoid: Replacement windows. What you have is better than anything you can buy once any needed repairs are made and air leaks are properly sealed.