Quit carrying mouse guns some years ago. Found my CZ Po1 and PCR will conceal quite easily under a loose t-shirt, even in summer time.
When I DID carry teeny pistolas, the fave subcompact was the KelTec P11 9mm, which rode as my backup on a body armor holster, too. The only micro I carried was a surplus CZ-70, (not made by CZ-UB/USA), in .32. Actually a very well made pistol,worked perfectly,(ignoiring the hard trigger pull), fed and fired HydraShok without trouble.