How can I fix my futon mattress?

Posted under sofa futon

I've been using my cheap, metal futon only as a sofa since I bought my bed a few months ago, but it's becoming less and less comfortable. The mattress is slipping through the crack between the back of the futon and the seat, and no matter which way I turn it, it keeps doing so. This makes sitting in it more painful than relaxing and I often find myself sitting on the floor instead. Is there any way to fix my mattress?

No there is no way to fix it besides gettin a thick mattress pad or buy a new thicker mattress.