I've replaced my elements with these
2 seats Carbon Fiber Universal Seat heater Warmer Kit Car Cushion - Round Switch | eBay

They are showing out of stock but there are several similar to these. You'll have to remove the seats, remove the covers.
The elements go between the cover and the pad. You can reuse the existing leads. It will require a cut a solder. Easy to do.

This brand was cutable which was perfect for fitting them between the cover and cushion