About a month ago, I got a Logitech M570 wireless trackball. It is incredible. A trackball, in case you didn't know, is a mouse that has a trackball that you move with a finger instead of moving your hand.
Logitech M570 trackball, from Amazon.
When I first used my trackball, I could not believe how comfortable it was. There was no adjustment period; I felt right at home using it. After a month of using it, I have noticed that my wrists don't hurt as much when using a mouse. The back and forwards buttons are perfect. I could not think of any ways to make this mouse better. However, like all trackballs, you need to clean out the trackball. This is easy on this mouse.
I would recommend this mouse to anyone.