A pillow mattress is actually a set of pillows put together to form one long mattress that is perfect for playing and lounging around. If you have kids in the house, this is something they will definitely like to lie down on. They can play on this pillow mattress, instead of their bedroom mattress (and spoiler the bed for that matter). The pillow mattress is also comfortable to sit or lie down on as you read a book or watch television in the living room.
Doing this is actually fairly easy, especially if you have the skills to sew.
The blog Southern Disposition has a step by step guide on how this can be done using duvet covers and five pillows from Ikea. The project is cheap and quick to do.
You can head on this the blog for the directions.