Good afternoon, folks!

I'm planning to use a SIG P938 pistol for concealed carry. It's still rather warm here so I'm planning for IWB or AIWB.

Problem Statement: most of the holsters I see for this model are of a "minimalist" design - just a kydex shell for the gun with a belt clip. While this minimizes bulk, I've got some muscle problems with my back and hip. When I try to wear one of these things, I wind up getting a lot of hip, back, and SI pain.

I've had success with holsters that have a wide backing (such as aliengear) but I'd prefer something with a whole-holster shell, backed by a soft, pliable material such as leather or memory foam. Bonus points if securely QD detachable.

Anybody have any ideas?

Sounds as if you're looking for something along the lines of a Crossbreed SuperTuck.

Take a look at the Hidden Hybrid Holsters. I have several for my different sidearms, and they're all great!

P938 models.

Black Point Tactical's leather wing holster should fit what you are describing

You might want to consider "Sneaky Pete" holster. Looks like a large cell phone case..

Linky.... https://sneakypeteholsters.com