My last car didn’t have heated seats so I bought an aftermarket plugin set. They were quite cheap and are really good and have been working faultlessly for 5 years.
https://www.ebay.co.uk/itm/2x-12V-NIVERSAL-CAR-FRONT-SEAT-HEATED-PAD-CUSHION-WINTER-WARMER-COVER-MAT-BLACK/312854073023?hash=item48d78e4ebf:g:~XcAAOSw~b1dlN8S