Moldy mattress! Don't know what to do?

So basically my boyfriends bedroom is in the garden in a little caravan, (No room for him in the house) The caravan could do with being burnt down because its falling apart but we don't have money for a new one. Its really damp with leaks, it smelly musty and heats up like a sauna in the summer even with windows open Needless to say its the perfect environment for mold. The boards under the bed are really damp, and the underneath of the mattress is thick in mold :O We have absolutely no money for a new mattress or bed and I'm really worried about it being dangerous to our health. The mattress is really thick and lined in this carpet-like material, it smells extremely fusty so my guess is that its grown right threw the mattress. Can anyone suggest to me any ideas about what to do? I'm scared to sleep on it but we don't have any more options. Also does anyone know of any health problems related to mold that we should look out for? Thanks guys,