Special Forces style seat covers.

[Tinstar]

"I’m sure you know that there are other seat accessory manufacturers out there. You can even spec out what you want."

Hey Mister Tinstar - Do you think any of those other manufacturers would consider sewing hidden pockets on the inside to hold heating elements? I don't mind paying for a custom quality product. Last time I checked, there was plenty of my daughter's inheritance left.[/QUOTE]

What they make fits over the existing seat.
Not the seat fabric/material itself.

As already mentioned, any really good upholstery shop can make what you want.