if your only putting down laminate this can go staright onto foam underlay, as laminate dont need joists etc undrneathe. i would suggest getting a builders film which you can get in any DIY store usuallu bout 40e a roll, this stop moisture from the flooe eating the foam,the foam underlay is bout 19.95 per roll. if your buying the laminate from a diy store most places throw in the underlay for free.
good luck!