I'm a retired LEO and while I'm new to making holsters, I'm an old hand at carrying. I carry a S&W 38 snubby and a little Ruger 380. I started making my own due to being a lefty and I didn't like what's on the market. I make my holsters for the front pocket since even my little 380 is tuff to conceal in the back pocket, also there are tatical reasons for wanting it the front. First I don't wet mold any leather in the finger guard or any tight place, also I don't mold past the center of the trigger guard. When I grab my gun I want it to come out of the holster. I have the grain side against the gun and the flesh side on the outside. This helps ensure a smooth draw and the flesh side provides friction against the pocket. Another reason not to do much wet forming is I don't want the gun "printing" on the pocket. The holster is supposed to conceal the gun not advertise it. I find no difference in comfort with having the back total flat vs somewhat shaped. I also stitch about a half inch from the edge, this way I can trim the holster if my new pants pocket is smaller.
I make mine from one piece of leather folded over and I have more the one holster for each gun. The reason for this is simple my pants pockets vary in size and so must my holsters. The commercial holsters are made one size fits all, that means they have to make it for a small pocket so it will fit any any pocket. When you use the holster in pants with a larger pocket it wont sit where you want it. It will flop forward or back or even on its side. Also I want the handle of the gun toward the top of the pocket so I don't have to dig down in the pocket to find my gun, more of a issue with the little 380.
Another problem that I'm going to have to tackle is sweat. It is highly corrosive and will quickly rust a blued gun. Since my 380 is blued its back to the drawing board. I'll probably need to make the holster in pieces. The back which is against my leg will be made up of a piece of plastic sandwiched between two pieces of thin leather. The plastic will act as a vapor barrier and hopefully protect my gun. The front will be a separate piece of leather with no vapor barrier. When I make a new pocket holster I wear it all day and until I go to bed for several days to see how the holster performs first is it comfortable if not it gets scrapped, I don't want to feel like I'm toting a gun and is the gun held securely and not shift around in my pocket.