such thing as a car seat cushion for LO bum?

[blazer_g]

LO loves his car seat and likes to have short naps in there (settles sooo much better and sleeps happily) but Im worried about his little bum on the hard plastic, I know he's only in there for a short time and I pick him up regularly to make sure he does get sore but is there such thing as extra padding or a cushion that can be used just for when baby is resting in the seat (I know it wud be potentially dangerous to use while travelling) just so I dnt have a reason to panic/worry lol. What has everyone found the best as Ive not found much on the internet Thanks in advance.