Welcome Merwin!
I'm not a fan of magazine extensions for anything short of an open gun. Basically, if I want a larger grip, I'd prefer to have a larger gun attached to it. With practice, you can learn to shoot well with the stock 19 grip length. If you just must have a longer grip, perhaps you could pick up a couple of Glock 17 mags. That gives you two extra rounds in a possibly more reliable package than grip extensions while giving you a rest for that pinky. Whether you decide to get a 17 or 19 the mags will be something you can use in either one. Good shooting! The Glock 19 is my favorite 9mm Glock.
Savage