Why not use a quality holster?
Something like a Galco Summer Comfort adds very little in terms of thickness and protects your gun's finish and your skin. It is much more secure and less likely to have you cough up your pistol when move around. Its also more stable, keeping the grip from tilting, letting you have a faster and consistent grip and draw stroke.
If you don't care about ease of reholstering, an even thinner option would be something like High Noon's Mr. Softy.