Damp on underside of mattress

Hi, sorry if i did’nt explain it too well.Basically, the foam mattress sits on top of the boards which has some kind of laminate cover to it. So they’re not slatts (wish it was). In each board have 7 holes in it, 6 small ones and 1 big one. Yesterday bought a new mattress (foam mattress) and throwed the old one away, lifted the mattress up today and saw sweat on 2 of the boards…what is going on???

Can i somehow customise the bed like put slatts instead of them boards or something?

And also i have no damp wall but sometimes the windows get abit cloudy. Please help, thanx. .