rear view mirror help

[jsm98r]

I have a 1998 silverado and I would like to upgrade my rear view mirror, preferably to one with not only compass but temp. Can anyone tell me how this works. I found some silverado mirrors on ebay with temp. and compass, do I just buy one of those and wire it in? Also, is the temperature sensor usually seperate than the mirror itself. Any help would be greatly appreciated.

thanks
justin