Have you tried the Logitech M500?
https://i.ytimg.com/vi/6qYHapP52IA/maxresdefault.jpg
The mouseman had the left mouse button perhaps an inch higher than the right. Net effect is your hand, wrist and forearm settled at a 30-45 degree angle, pretty close to the natural rest position. That;s the bit I miss - it was really comfortable for long use.