Flat cushion (3)
I believe the answer is:
pad
I believe this is a double definition.
'flat' is the first definition.
(a person's home)
'cushion' is the second definition.
(to cushion something is to pad it)
(Other definitions for pad that I've seen before include "Helicopter stand" , "Walk with soft steady steps" , "Footprint - home of one's own (slang)" , "Floating leaf of water-lily" , "Sports guard; home (colloq.)" .)