My considerations for AWIB carry, my body type is tall and slender:
In order of priority,
1) safety, for me this rules out short trigger, zero manual safety SFA's
2) barrel length for comfort down there...
3) slide and overall thickness
4) Butt length
A lightweight commander would fit the bill and maybe someday I'll get one in 9mm/.38 Super. Right now my new to me Beretta 92c works well in all areas except thickness. I use a Wilderness Tactical horizontal mag pouch.