I've been carrying IWB for more than a decade. In that time I've learned some valuable things (things that I don't think those that hate IWB carry have).
1) You MUST adjust your wardrobe to accommodate the gun. Pants an extra couple inches at the waist and a quality gun belt.
2) A dual clip/loop type holster (like the much loved Crossbreed Supertuck) will carry even a full size gun comfortably ... a single loop/clip type holster is ok for something slim and tiny like a Kahr MK.
3) 3:00 is more comfortable than 3:30 or 4:00, plus your arm covers it aiding on concealment, plus you can draw while seated in the car.
I'm willing to admit that there probably are a few people that just can not make it work with IWB ... but the vast majority of those that I've met over the years that tell me they just flat couldn't make if comfortable didn't wear larger pants, didn't have a good gun belt and were trying to conceal a full size gun in an Uncle Mikes POS hoster (the goofy one with the mag pouch on the front).
As for what holster is best, I would say something like the Crossbreed Supertuck would probably be the best out of the box solution (I don't own one, but I have used the Crossbreed clips on one of my holsters).
For years what I've done is got quality, custom made leather pancake holsters and then affixed steel spring clips to them with chicago screws.
Like this: