You might still consider mice, as there are Trackball mice which are similar to normal mouse precision but operate in a different way:
This for example is the "Logitech M570 Trackball". Basically instead of moving the mouse on your table you move the Trackball with your thumb. Your shoulder does not move a bit.
There was once a top professional Counter Strike player that used a similar mouse, but I forgot his name, which proves that you can make it work even in precision games that require fast reflexes. Here is an old discussion about this topic: Gamespot Thread
This does not really concern your question, but I guess you are using your mouse in a wrong way. Day, a professional Starcraft veteran has a 1 hour show that explains how to correctly use your mouse and keyboard for Starcraft 2. You can easily adapt this to Diablo 3 or any computer game. Check it out: Day9 Daily 252.