I'm a little younger than you are ...and have some arthritis as well in my hands....
a. Nothing wrong with a revolver. I think a mid-sized gun chambered in .357 mag ...and you can either shoot .38 spl's or .357 mag in it will be fine. By mid-sized I mean something like a S&W K frame ( model 19 or 66 ) ...and while some may have traditional wood S&W grips on them / some of them will have typical rubber Hogue grips on them ...dampening recoil a little as well. But the weight of the gun is your friend ..in terms of reducing recoil...and then picking the right cartridge. 158 gr in either .38 spl or .357 mag are very common cartridges. These K frame S&W's will come in 2 1/2" barrels, 4" barrels and 6" barrels....but I think a 4" is probably a good compromise...not too heavy or clumsy.
b. If you want a semi-auto ...stay with something in a 9mm. Again a gun with some weight is your friend. Arthritis - might mean you have to stay away from guns that feel too wide ( many guns in 9mm today - are double stack mags / where they increase capacity) but it makes them too wide.
A gun that is commonly available ...is a Sig Sauer 239 model ....its a single stack gun ...available in a couple of trigger options / I like the typical Sig DA/SA trigger with decocker. They hold 8+1 ..and they nice guns. They come with a hard plastic grip on them ...but again, consider putting a Hogue rubber grip on the gun ...with or without finger grooves. Personally, I like the Hogue with finger grooves. Helps me stabilize the gun a little. On days when my hands hurt a lot ...Sig 239 is still a gun that makes it easy to reach the controls. Again pick the right cartridge in a 9mm ....like a 124 gr bullet ...vs 115 gr or 147 gr...I think most 124gr rounds in 9mm shoot a little softer ...than the "snappier" 115 gr or the 147 gr rounds.
If you don't like the Sig - look for other single stack mag weapons...( 1911's come in 9mm as well ...from Springfield, etc ) ...but they're more money.
and good luck in the process ...and have some fun with it..../ shoot as many guns as you can at ranges that rent guns, or maybe your buddies guns - before you decide.