Gas heaters have not increased equal to electric but gas is still more effecient than electric. At 20 years old,you are overdue for the heater to fail so it's wise replacing it now.
Water slow to get hot on secound floor has some options to choose from. The best would be a secound heater upstairs but cost can range from reasonable if gas supply is adiquate upstairs and plumbing is accessable in right place to expensive if new supplies must be installed,not to mention suitable space to house the heater. A circulating pump is inexpensive to install while changing heater but I reccomend researching shortened life of water lines using a pump. If your daly routine is consistant,I suggest a timer that runs pump only during peak usage of hot water. I have set a few up with timers that start pump 30 minutes to 2 hours before resident's normal showers then remain off majority of day. It isn't difficult for an electrician to install an override switch next to where hot water is needed off peak ocasionaly . 3rd and cheapest albeit less effecient and reliable than other options is a point of use electric heater.

Ideally, you'd like to recirculate to the most remote fixture, but if there is a 1st floor fixture in a close proximity too the 2nd floor fixtures, it's half the battle.
Depending upon your heat plant and the return air plenum, you may have an easy accessible conduit to the upper floor fixtures.

I appreciate the guidance. I hadn't heard of the recirculation pumps before, so will definitely explore that option.

It's more than a pump, it's a system which requires a return line too the heater.
However, there are those which can be connected at any fixture, which connect between that fixtures supply lines.

Search this forum for Laing and Autocirc

Retrofit recirc pumps that are affordable and easy to install.

Watts makes one also.

If you are not oppossed to electric many power companies will give a free replacement or large discount if you convert from gas to electric.