I'm going to peruse the various holsters described above because I'm always exploring holster options. I recently acquired a Bianchi 3S IWB but haven't used it yet. However, there is comfortable, uncomfortable, and, well, maybe something closer to comfortable than uncomfortable?
Years ago there was a store in Dallas called Wald's Police Supply. The proprietor happened to have designed his own holsters, among other things. The one I am using today, and have been using for a long time, is as close to comfortable as I think you can get.
First, the gun. My EDC is a Model 10 snubbie. Larger guns are almost impossible to make IWB comfortable. Even my 6906 works hard to be comfortable.
The holsters I use for the Model 10 2" include one "Wald" IWB that works perfectly. It is made from very soft leather and the gun fits into it perfectly, like skin, in fact, because it is so malleable and so perfectly formed. Because it's a snubbie, and because the single metal clip rides high, the gun vanishes inside the waist band of jeans, casual slacks, etc. Naturally, you cannot be wearing tight pants when you do this.
Basically, a thin, soft leather holster with a single, high riding clip, holding a snubbie revolver, is as close to comfortable as I think you can get with a gun beyond mousegun caliber.