It's certainly not a bad idea. Reinforcements are almost always found in queen and king beds. It depends a lot on how strong your box frame is and how much weight you'll be holding on the bed. I'd feel better with a little more support. Kings always and queens sometimes have "split box springs" that make a center support mandatory.

The strip your guy recommends is called a "ledger strip." Generally these are 1"x1" and are screwed every 6-8 inches across its length.

Typically 1x2 are used for cross beams and these are screwed down into the ledger strip. I've also seen then dropped into a notch, but this is both more work to build and less secure. Sometimes they are stapled to a set of nylon straps. Don't really think the staples do much but hold the spacing. They are certainly of no structural value. I have seen cross supports every 4" or 4 per bed. I think the choice is yours.

As far as a center support to the floor, I usually see one or two of these in kings. I have cobbled together supports like this with a flange, cap and iron pipe nipple from the plumbing department. I've also seen a 2x2 cut to the right length and bolted into its cross beam with a dowel screw or hangar bolt and t-nut. The link below shows hardware specifically for this purpose.

The little attachment on the sides is mean to hold a notched out beam that goes left and right.

Here is a link that might be useful: Rocker premade bed hardware.

well- here is my two cents- if that is really an antique- any modifications will devalue it. so this is my suggestion. build a bed-within-the-bed. make a frame that will sit on the floor inside of- but not attached to- your bed. the mattress can now sit onto the new frame and you will not harm the value of your bed by making modifications.

"if that is really an antique- any modifications will devalue it"

That is rarely the case.

The platform frame is not a bad idea, but unless this is a museum quality piece, I don't think simple structure reinforcement is going to affect the market value to a knowledgeable buyer. Antiques Roadshow has created a whole class of society that is blinded in the headlights because they believe simple repairs will destroy the value of the piece they just spent $500 on. Often the opposite is true -- not doing repairs will accelerate the demise and loss of value. [ stepping off soapbox ]

I am not speaking of repairs. I own a woodshop and I make good money restoring and repairing antiques. what she is talking about is a modification. which i would never endorse with any of my clients (although i have done it when it was insisted upon). there are almost always alternatives. but i do agree with you about repairs, if they are needed they should be performed [falls off soapbox-lol]

I have an antique bed and use wood supports. My bed frame already had a ledge to hold the boards so I didn't have to modify. My experience is that most antique beds requried some modifications for modern use and it often wouldn't decrease the value. Just my two cents however. I have lots of antiques and rarely modify except for beds.