Yeah, there should be plenty of info in this forum on BKK airport hotel (or is it in the TG forum?).
Anyway, with 12 hours I would certainly book a hotel room, but not at the overpriced Novotel BKK airport. If you only want to sleep/spent time in the room I would choose one of the many adequate hotels in the airport area (many offer shuttle service, but otherwise a cab will be cheap in BKK)