I tried this recently and got fairly bad pain in my thumb (bottom towards the palm area). I’ve since switched back to just using my old vertical mouse and the pain is gone. It’s a shame because I did get used to it and quite like using the ball.
Maybe try a Kensington Expert Mouse [1]. I use these a lot. I'd suggest the wired version - the wireless one seemed to interfere with my Bluetooth keyboard (probably the keyboard's fault though).
I've used the Kensington SlimBlade for years and really love it. The only difference from the Expert Mouse is that instead of a scroll ring you just spin the ball in place. Completely eliminated the RSI I was getting in my mouse hand and is my favorite hardware for mouse-like functionality.
