kydex is thinner than leather. check out rm-kydex, bearclaw holsters, dan hillsman holsters, comp-tac, cross-breed, and other makers of custom kydex holsters.
Below - profile on a BearClaw Holster's "Hidden Asset" IWB. The only thing that could be thinner would be mexican carry or clip-draw neither of which are options that I will consider. A holster not only covers the trigger for safety' sake, but a holster also keeps perspiration and moisture off of the gun.
EDITED - My sideguard is also very thin: