I sometimes use a Belly Band, inside my belt line. As was mentioned earlier, it can help with stretching and such-- even for those of us with small waists/lots of room to cinch.
Over time, I have used mine to carry a PF-9, LC9, and SR9c. I have even put my PPQ in it a few times. The SR9c and smaller options are very comfortable in it.
I think that the perfect deep-conceal option for a BB is probably something like a Walther PPS, S&W Shield, Walther PPK/S, or Bersa Thunder 380. Something slim through the slide, but with a grip long enough to easily secure purchase on for a quick and clean draw.
I would probably not carry steel in one, in order to preserve the band.
Currently Own: Beretta PX4 9mm, Glock 23 (Gen 4), Glock 19 (Gen 4) x2