380 is considered the minimum by most. As you read, one forum member carries a 32 and doesn't feel under armed. The confidence in your gun is important. Getting your hits with a 32 or 380 is more important than misses with a 45 or 357.

That being said, my wife's Sig 232 in 380, to me, recoils more than my M&P compact in 40 for roughly the same size gun.