The G19 & CBST is an excellent combination for carry. At least, it has been for me. I avoided Glocks like the STD of the gun world for many years. Then I bought one about a year and a half ago, and as much as I hate to admit it, my G19 gets more holster time than any of my other carry guns at this point. I follow the "carry the biggest gun that you can carry comfortably" line of thought, and the G19 fits that model. It's large enough to shoot well, small enough & light enough to carry easily.
If you're going to go IWB, I do suggest a CBST or some other kydex/leather hybrid. If you simply have to have an all-leather IWB, get something with a reinforced mouth. Otherwise, the tension in your belt will close it up every time you take the gun out of the holster (as tomrkba points out happens with his holster). The CBST's kydex shell doesn't suffer from that.
If you're going to carry, let me also suggest that you invest in a good gunbelt, if you do not have one. Having a proper gunbelt makes a huge difference in ease and comfort of carry.