That, too, depends on individual choice, though medical opinion usually favours the hard mattress.
They can still sleep in comfort because one half of the bed has a hard mattress, the other soft.
None of it was real, he thought, and slid down again on his hard mattress.
The same is true for sleeping on a hard mattress.
It was a peasant bed, a hard mattress in a corner.
Beds should be comfortable, with a good, fairly hard mattress.
Making Natalie sleep on her back on a hard mattress wasn't enough as she got older.
He fell with his full weight into the hard mattress and slept.
The back pressure resolved itself into the fact that he was lying face up on a hard mattress.
It was made of flat steel slats with a thin hard mattress over them.