scroogle.com and scroogle.org don't appear to be affiliated, the former being porn-related, the latter being the search proxy.

I've got an E-Quill AirO2bic vertical mouse. It's basically a mouse turned on its side, with a 'quill well' (marketing lingo for 'hand rest'). This lets you move the mouse around without using your thumb for grip at all. Probably best if you visit the site. They'll give you a better description, with pictures.

It's perhaps a bit expensive, for all you're getting, but I found it helpful, so there you go. Worth the cost for a bit of comfort.