You have to be careful if you fit seat covers. The side air bags need to be able to deploy in an accident so seat cover may hinder this. Better to get a good upholstery cleaner and periodically clean them thoroughly.
But if you really want good seat covers then the only ones I would recommend is LEATHER...
It would seem a better tactic to me to replace the whole lot with a darker set of seats. Always cropping up in the Marketplace on here free or for peanuts for cloth, somebody may be even interested in your what sounds like your Twist seats.