I've had various pocket holsters. Most have that 'hook' to keep the holster in the pocket. Most are rather thick in the pocket, IMHO.
Just take a look at the Fist kydex holster...see 'Related Links' above...just look at it.
It has a thumb push which guarantees that the gun comes out and the holster stays in the pocket....very thin, and very stable (gun won't tip in the pocket).
It costs you nothing to look...

...it's the only pocket holster I will not use.