Thanks for the responses. I have done some reading on the issues, reorganised my desk paying attention to advice given above about arm placement and decided to go for the A4 tablet which I understand will give 1:1 mapping. Currently it all feels very strange!
Having a pen adds another implement which ought to reduce some of the repetition. Also being left handed, but have become accustomed to mousing with my Right, it will enable me to spread the load still further.
If it didn't hurt so, my fingers would be crossed!