The mousiest that I CARRY now are a Kahr PM9 Covert and a S&W 442. That's as small as I've gone for a long time.
But when I lived in the Chicago area and couldn't carry a gun, I found a Beretta 21A .22 awful handy at times.
The only other mousegun I have now is a Walther TPh .22. It's mostly for fun. If I were to carry either the 21A or TPh now, it would if I wanted something like a fourth or fifth gun!