I have a '95 850 GLT, sedan.

Recently, to replaced the cracked and weathered leather seats in my car, I found a pair of front seats in a junkyard from a wrecked car. All was well, they mounted up without incident. It turned out the seats had heaters in them. I found my car to have the wiring harnesses present under the seats and in the console as well. Popped off the switch blanks, put the new-to-me switches in their place, and in 15 minutes had heated seats along with un-cracked leather. All in all, a good project.

Check a local salvage yard, they may be able to help you out with the heating elements and switchgear.

Your car possibly has the wiring in place and just needs heating elements and switches.