I always keep a huge bolster cushion under my wrist when I'm using the mouse. It works wonders, far better than any of the smaller cushions I've seen on mouse pads.
A good exercise to relieve carpal tunnel is to hold your arm straight up from the elbow, and rotate your wrist. I do it in both directions, both with fingers open and closed in a fist, and I put some serious energy behind the movement. It does seem to help me. Hope it helps you, too. 🙂