That's an expensive fix any way you slice it. Choices include:
1. Find a nice spare set of BMW Sport seats? I'd estimate at least $500 for just the seats, though they come in a wide variety of coupes and 'verts. A whole matching 'vert interior is rare though...prices tend to be high.
2. Custom re-upholstery...price and quality vary widely. But you can pick your fabric!
3. Stock BMW covers. I'd think about $1000 for the four front covers and maybe $300 to get the properly installed. Unless they're NLA, which is likely.