We only use a "seat cover" when returning to the car after playing golf or if we're wet when it's raining outside.
Rather than spending a lot of $$$ on seat covers we only use for short periods, we purchased two large ultra white bath towels and installed snaps at one end of the towels. We place the end with the snaps over the headrests and have the rest of the towel cover the seats.
And when we're done, we put the towels back into the left side of the trunk, in the space that goes down towards the underfloor storage.
Not elegant - but gets the job done... We've used the same solution on our S P85 for the last 4 years...