So I wanted to upgrade my cloth interior, what other makes and models will fit an SL1 ... front seat and back seat? I'll be looking for a leather interior from another vehicle but I don't know which ones are compatable.

You have posted in the wrong model forum and may be the delay in a response however..

http://www.saturnfans.com/forums/showthread.php?t=99019&highlight=seats

***Moved to correct forum***

if you are still looking, try to find a SL2 donor, better chance to find leather and in some years the SL2 had better shaped headrests