The grip diameter on the 19 will be the same as the 17. If you want a smaller grip size, look at the Gen-4's with the interchangeable backstraps. I have the same problem and the Gen-4 solved it for me.
“Neither cold, nor darkness will deter good people from hastening to the dreadful place to quench the flame. They do it not for the sake of reward or fame; but they have a reward in themselves, and they love one another.”