The pillows that they made from the same material were in pillow cases and you could still feel it through them pretty easily. I doubt a sheet would help for the mattress. A mattress pad might be enough to cover the gross texture, but at that point you would have wasted money buying a gross feeling mattress when you could have bought one that didn’t need a mattress pad to feel like a bed.
Steampowered Giraffe reminds me of a friend who died a couple years back because she really loved them.