I used to put down a flat terry nappy on the reclining seats before DS was sitting up on his own but that was also to stop any of his spew getting on the seat lol!

Since he's been sitting up I haven't bothered buying one of those covers because a) I'm lazy and can't be bothered taking any more gear to the shops; b) we have pets he touches, he eats off the floor when I can't stop him quickly enough, sucks other kids toys at mum's group etc etc and c) he has a cloth nappy which seems reasonably comfy like Nai said.