Blimey, sorry to hear that Tom.
Not sure if this is helpful, but I used to fluctuate between trackpad, intellimouse and a wacom tablet to introduce variance, but for the last year+ I've been using the Apple mouse, which has caused me no discomfort whatsover,
I think it's because my hand doesn't settle in one fixed position (as with the other devices), and so I think it's the most comfortable device I've used.
Rest up - hope your hand recovers quickly...