Check out Kramer gun Leather. They use Chicago screws instead of snaps, so you can't take it on and off, without undoing your belt, but I haven't has much luck with any IWB doing that really well anyway.
As for your concerns of the gun sliding out... I think you're worrying about MOSTLY a non-issue. It's not unheard of, a guy lost his pistol in a movie theater in Oregon recently, and it was found by a couple kids on a field trip that had some Eddie the Eagle training. But that's the only story I've ever heard of a guy losing his concealed carry while carrying. Sure you get used to having it there, and eventually stop pulling your pants up every time you stand up or get out of the car... but I still have a pretty good idea that I have a several pound handgun hanging on my belt.