Do your holsters have bodyshields (extensions of leather between your body and the rear potion of the slide, hammer, etc)?
All of mine do, so the mag release is effectively guarded from the shifting of my spare tire as I go through daily routines.
The bodyshields quickly contour to, and reinforce, the position of thumb safeties, too.
You can see part of the bodyshield in WVSig's 1911 VM2.
Sam Andrews, Mernickle, High Noon, El Paso Saddlery, Soteria Leather, and many others offer bodyshield options on holsters.