Do a search for the Evoluent Mouse.  It works in a vertical "handshake" sort of plane.
https://www.aulro.com/afvb/images/im...014/09/823.jpg
I had bad RSI on my index finger (switched mouse hands for 2 or 3 months to let it get better) and then I came back to this.  Mine is set up with one button to double click automatically, so no need for double clicking manually, which takes a lot of strain off the index finger (as you are using another button altogether with your 3rd finger - if that makes sense).
No problems since.
HTH
David
Edit:  Just to say, it is as accurate as a normal mouse.  Like Ron, I tried a trackball but it never really did it for me....