People on the Briskoda forum a few years ago were raving about Seat Surgeons in York. Apparantly good service, and excellent workmanship (photos look great!). I'd say its definitely worth calling them up and getting a rough quote. You'd end up with bespoke leather in practically whatever colour you want, and the door cards too. Maybe they can even install heating while they're at it?

I haven't looked at the idea since my last car, but I am very tempted myself for the Mazda.