If you've never carried IWB before, you ought to borrow some you can try for an hour first. Reason being, there are two major platforms... the regular style holster like all those in the pics, and the "Crossbreed style" with the large (5 x 10 inch or so) backer panel.
After dropping $10 here and $30 there and finally $70 on a Bianchi, I finally decided IWB was just too uncomfortable. Then I heard testimony about the comfort of the Crossbreed, Alien Gear, SuperTuck, etc. style and decided to try one. After a little research, I settled on the all-synthetic Stealth Gear model, due mostly to the testimony of guys who wear it in hot, humid climes. I bought one for my 340M&P (pricey at ~ $100) and have no regrets.