When I made the toy basket from the cradle I was left with a mattress with no home. I could not throw the mattress out, like I cannot with any craft item, and needed to place it somewhere. It does not fit in my crafts cabinet and so I decided to recover it with nice fabric and give it to Likka to use. She can later perhaps lay on it, while drawing, painting or "reading" or what ever children happen to do while then don't run around.
I covered the mattress with the carrot fabric from an old sheet which I have used before on Likka's stuff too, like for her duvet cover. The black zipper is from an old shirt of mine. So far Likka has not been too interested in the mattress, so I hid it in the toy basket. It's there out of the way but available when even these sort of things like pillows and mattresses start to interest her.