mattress

nouns

a large thick pad filled with resilient material and often incorporating coiled springs, used as a bed or part of a bed
mattress
is a part of
a piece of furniture that provides a place to sleep
"he sat on the edge of the bed"; "the room had only a bed and chair"
bed
is a type of (narrower)
a flat mass of soft material used for protection, stuffing, or comfort
pad