Hey Don,
I shoot only with a tab and have had the same problems as far as what size to order. I would rather order one too big and trim it down then order them too small. I have a handful of tabs including the blackwidow, the mitt, and a few others. however all of those are in my backpacks as spares and I only use a single piece of tough leather that was made for me in 1995. I'm still using that tab and it has a lot of life left in it. For me a simple piece of leather works great, is cheap, and last forever.
Good luck,