We had heated seats added with leather interior, both by Classic Soft Trim. I believe the cost for the heated seats was $300. I also remember seeing products for DIYers at the same site that had the lumbar support that some people here have installed. Unfortunately, I don't remember who it was, but it is probably in the Tech section.
'01 SS EX
Cassette, Rosen Video System, Fog Lights, Splash Guards
Full Nose Mask
See photos at: