Hi s.guo1,
That’s a good question. Usually the compression, if any, is quite minimal in the items you described, and the covers, while relatively snug, float well over the foam on the inside. You would have some sewing to do with replacing the cover.
If you want to avoid a used item but instead want something new but affordable, then post #4 here and the posts it links to also include many of the better lower budget online options I’m aware of.
Phoenix