Just wanted to mention something I learned at the April 2021 Fiddle Hell Festival.
Cello Workshop Instructors, as well as participants, were ALL raving about how great the "Stringvision Bowgrip" is!
This is a very simple little frog covering - very sleek/nice looking. The material keeps your fingers from slipping and there's a nice little dimple/divot for your thumb!
I seem to remember you asking for suggestions to add items to the Fiddlershop, but can't find that thread.
I don't own one, but after all the trouble I had finding a bow with a good resting spot for my thumb - I think my playing would have sounded MUCH better with a much more relaxed bow grip, EARLIER... if I'd just had one of these!
This Bowgrip by Stringvision might be a great item to add to your inventory.
This is elegant and stretchy, so fits over all Cello, Viola & Violin bows!