Hands down, the best IWB holster I've ever tried is the Tucker Answer.
It has a leather backing, but that is lined with a thin layer of chrome tanned suede, which both feels great next to the body, and because of the bonding, prevents sweat from reaching the gun. Because it is chrome-tanned, it is nearly impervious to the effects of sweat and body oils. The nap of the suede on mine has stayed soft and comfortable for over a year of daily wear.
They have to be tried to be believed. It really is, "THE Answer".