Japanese mattress (5)
I believe the answer is:
futon
'japanese mattress' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for futon that I've seen before include "Padded unsprung mattress" , "A Japanese bed-mattress" , "Mattress used as a bed or sofa" , "Type of sofa bed" , "Japanese sofa bed" .)