A deep and thin skinned iwb holster made out of calf skin is the best way to hide a full size gun. The calf skin is thin and doesn't add to the width much, is soft, and conforms to the body while adding cushion.
The deep carry mode puts the butt of the pistol right along the belt line, doing a great job of hiding it. The down side is since it is carried deep, a quick combat or shooting grip will not be possible. You have to pull it out with the fingers and then grasp.
I carry a g17 and 1911 this way in a holster I designed and had made by a local custom leather man here locally.
This is the very best way I have found to carry a big gun in relative comfort all day.
I prefer this to any carry mode that has the gun pointing at my " junk" in the front.