I've an idea for you, it's what I'll be doing
I have a Logitech mouse, of the sort meant for gamers even though I am not one, which I picked because it fit my hand perfectly and allows my it to rest completely on the mouse, from the heel to the fingers (my hands are pretty long

)--this is just the right size and curvature for my hand to rest on naturally, and allows me to reduce the number and scope of the movements my wrist has to make. I bought it to go with my Windows laptop, and decided to keep it when I got my lovely Macbook two months ago for the sheer ease of fit (I had given myself RSI, carrying bags of groceries home if you can believe it, and using the proper mouse kept me from straining my wrist even more lol)
But it is kind of ugly, and hogs one of my two USB ports since it's wired. Plus, I hate having to drag the bulky thing along when I take my Macbook to a cafe or somewhere to sit and work (can't go mouseless I'm afraid). So as a treat, once I've finished a big, boring clearing out job I'm doing now, I'm going to get myself a wireless Mighty Mouse, to use when away from home and when I want to have both USB ports free, and keep the Hog for good ergonomics

.
But I can do that as it's only an extra luxury sort of thing--a reward. If this is going to be your only, or main, mouse, I think it could be wise to make getting something that's right for your hand your main priority
