Mx Ergo is great as a thumb trackball, the Kensington trackballs are well reviewed, elecom has the giant mice and I think l-trac mice were bought out by x-key and they still exist and you have ploopy that came out of diy from Reddit.
And I wouldn't recommend it, I end up having some pain in my right thumb, that stopped when I stopped using it.
However this is just my experience.
I never had any problem with any mouse, it is the fact that I need to move the thumb so much. Also I might have a job which is more intensive in mouse than most people coding.
Or perhaps is that the "celtic hand" runs in my family and it is not good to use. I am afraid I will have to sell it, which I don´t particularly like because it costed me quite a lot.