Not ideal for gaming but Trackball could be good
Otherwise, i'm not sure. I used to have a Naga and that thing was bliss for comfort. Coming away from that thing was like giving up heroin.
It might take a while for you to get used to another mouse but you never know the benefits until you try. Just get one with a nice sensor that you think looks good.
I have a SS Sensei and tbh it's quite large, maybe go for the Zowie like you were planning or perhaps a Deathadder. Both sensors are top notch and the Deathadder must be most popular for a reason, right?
I'd give it a go.
On topic though, if you haven't experienced this before with this mouse and it's only just started happening, perhaps it is something to do with your posture etc. Trying doing finger/hand exercises perhaps.