Well, my 280 is 19 years older (78 280E), but I'm going through the same thing, as the PO was a little soggy around the midsection. I removed the seat and took a look at the underside to see what was doing, a few broken springs, very old horse hair mat, the usual problems. It didn't look too easy for someone at my skill level to do myself.

I asked my mechanic if he could recommend an upholstery shop, went down there, guy said $100, with parts and labor. That sounded just fine to my ears! The actual procedure only takes them an hour or two, I guess, the only downside is there were no openings for three weeks! Anyway, you might call around the auto upholstery shops, they could be very cost effective. Hope this helps

Simon
78 280E "Sally"