I made this pocket holster back in 2009. The body of the holster is formed around the gun but I kept it loose, because to much retention with a pocket holster could be a problem.
The main design challenge you have to overcome with a pocket holster is two fold; (1) keep the gun from rotating in the pocket so the grip presentation is predictable, (2) make sure the holster stays in the pocket when you remove the gun.
My solution incorporates a snap on outside cover, at first glance it might seem that this is just to help the gun from any unwanted print through. That is part of its job, but the main one is to keep the gun from tumbling in the pocket and help keep the holster behind in the pocket when you draw your weapon.
I usually shipped this holster with two or three leather covers with snaps. One of the covers was trimmed out to fit a common Levi jean pants pocket, the other covers where left untrimmed so the user could shape them to fit their pockets. When the user controls the actual profile of the holster he is better able to insure proper fit and performance for various pocket sizes. And the snaps make it possible to quickly change the holsters profile for various types of pockets.
Just for good measure I added a little extra piece of leather across the mouth of the holster to help keep it open for re-hostering.