So I decided to split my foam mattress in half (to make it easier to store/transport and no fold crease in it) and make a cover for it, so I used the old sheet it was wrapped it and got to work!
Now, I'm not very good at sewing (at all!) so I used the below pictured heat bonding iron on stuff to hold the whole thing together:
I then ironed on some velcro strips to be able to close the flap to contain the foam, and to also stick to each other so that the two seperate pieces of foam don't slide away from each other during the night.