DD just got a hand-me-down bed from a neighbor. It has a trundle drawer underneath and we need a mattress. This will get occasional use by children. We doesn't need anything fancy, but something that friends eventually will use for sleepovers and that her brother (7) will sleep on when we have houseguests in his room. DD is 4 now.
I'm looking online and it seems difficult to find the trundle mattresses.