Fount damaged mattress (5)
I believe the answer is:
futon
'mattress' is the definition.
(futon is a kind of mattress)
'fount damaged' is the wordplay.
'damaged' indicates an anagram.
'fount' anagrammed gives 'FUTON'.
(Other definitions for futon that I've seen before include "Japanese matress-bed" , "Padded mattress for sleeping on the floor" , "'Japanese mattress, can be folded (5)'" , "Japanese mattress with frame, a bed-couch" , "Kind of Japanese chair-bed" .)