D'Andrea parti-colored thumbpicks are looser and easier to re-form. Many people like Fred Kelly's, but they seem small to me and bite my upper thumb.
Propik makes a thumbpick with a metal band attached to a plastic picking blade, and it's pretty large, and bends easy partly because the metal band has an open center, on the theory it grips better--might help with the circulation. I can't use any of these, but make my own so the pick tip runs parallel with my thumbtip.

   Steilberg strings in Louisville sells lefties, and I'd think somebody would have them so you don't need to bulk-order. Have you checked the websites?