There are a ton of compact and sub-compact autos out there that would fit the bill for your Dad. For carry I like my Glock 26 (9mm sub compact) and I have shot the Glock 19 (9mm compact). 9mm ammo is cheap and does not have alot of recoil so you can have fun with it, even out of a smaller framed pistol. I am a small guy and I can shoot the 26 all day long and not regret it the next day. I'm sure you will hear from people recommending Ruger SR 9 and SR9C, Springfield XD 9, Sig Sauer P228, try to handle if not shoot several before you buy. They are all good options. I just had 2 friends buy the XD 9 and XD 9 subcompact and they love them.
Right before you specified the New Service .45 Colt, I was picturing a Smith and Wesson .357 with a 4 inch barrel. Then you could target shoot with
.38's if you wanted, and there are a ton of options if you did get into reloading.
Only you and your Dad can decide whats right for you, but there are some options.