I use to carry a Beretta 84F in a left holster in my vest under my left arm. It's 13 shots of .380 cal. or (9mm short) and one great shooting handgun.
Then I had a Beretta Mod. 70 .32 cal. in my center vest 8 shots for close up and personnel defense.
Now at my present position as a University Police, I don't carry any backup. Don't feel the need to at this present time. I hope that helps you out on making your decision, there are many good backup weapons, good luck.