Unless you are well trained and practice at least monthly do not go with any weapon other than a revolver. They are the essence of point and click simplicity. With an auto you have to think about too many things (is there a round in the chamber...is the safety off?) Get the revolver that fits your hand but do NOT go smaller than .38. S&W makes a number of nifty small frame five or six shot .38s. They are all reliable and accurate to 15 yds. (The average encounter takes place within seven yds.) NYPD used a .38 Colt with ball ammo for over a century and NEVER had a malfunction. Go with pre-fragmented hollow-points using a low load. They pack a punch and you won't have through-and-through issues.
If you are a big person and get the training then think about the M1911 .45. Almost any variation from a reputable mfg is good, but costly. Even then there are recoil, stovepipe and over-power issues.
Ignore anyone who praises riot or trench guns. I have never heard of any instructor or experienced officer who opted for any shotgun as his first choice. They are two-hand weapons...not a good idea in the dark, coming down a narrow stairway or turning a corner. Leave them to the SWAT teams. Besides, where in the bedroom or the car or your bag are you going to keep a shotgun?
Ignore anyone who tells you that a .22, .25 or .32 is acceptable. I personally know one dude who got shot SEVEN times with a .25. His street name is Champ and he's still around.
Ignore anyone who tells you to aim for a head shot. You're not a Mafia hitman. No professional will ever train you for this. Just take a look at qualifying targets...no points for a head shot. Two quick ones to the center of the torso ends all arguments.
Whatever you do get, keep it clean, learn how to use it, stay practiced, and pray you never have to use it.....good luck and God bless.
I am shocked that no one has taken you to the woodshed for mentioning S&W without (what some around here consider to be) the proper amount of hatred, though.
If everybody always repeats the same advice most people simply accept it without thinking. You give us a few things to consider, and as a former LEO you probably have thought about what you posted.