XJs had heated seats, at least the limited/classic trim levels with leather seats did, there's one in my driveway. The leather power seats sit up higher than the manual seats, they're comfortable seats, but for 6' (34" inseam) me to fit comfortably, they need to be about an inch lower and an go an inch or two further back.
When we moved to Columbus, OH in Fall of '10, we moved into a townhouse with a single car garage. You can guess who got to park in the garage, SWMBO. By Thanksgiving that year, this poor Southern boy had a heated driver seat and remote start in his Volvo 850.
I used this Dorman, kit, and a junk yard 850 seat heater switch. The kit comes with a switch, but I wanted a more OE look install. I only did the driver side, SWMBO often reminded me of that fact, but I hardly ever rode in the passenger seat, so I didn't feel it needed to be warm. Install was pretty easy, I pulled the seat, stripped the leather back, stuck the heating elements in, and reassembled. Still works great.
I used a Python/Directed Electronics, I think Viper is the same thing, remote start kit. I did the install, it was a bit of a challenge, fooling the car's anti-theft immobilizer, and integrating it with the keyless entry. If I had it to do over, I'd get a simpler system that was remote start only, and use the car's OE keyless. It worked flawlessly for about 4 years, it's a little flaky now, I've not attempted to diagnose it, but I never use the remote start feature anymore, since we've moved back to AR.