Have you considered a small revolver? You'll find them to be extremely reliable. Pull the trigger...they go "boom". Don't have to worry about safeties or feeding issues. Get one with an external hammer and, if you have time, you can cock them with your thumb and have light single action trigger pull. BTW: Get a .357 and then you'll have more stopping power than a 45, .40 or a 9mm and you can shoot 38 Specials or 38 Spl +Ps if you want a little less recoil and report.
When I was carrying, my gun was a Smith and Wesson Chief special with 200 gr loads. I loved that piece. Wish I still had it.