Hmmm...perhaps I'm stuck.
Theoretically some of the slats would line up with each other and provide some support down the middle, but it sounds like it needs a LOT of center support. I'm not familiar with these mattresses, so I'm not sure how the weight distributes. It seems like such a large mattress would spread out the downward pressure a fair amount and that the combination of slats, cardboard, frame, center beams, etc. might spread out the pressure enough, but it sounds like that may not be the case.
Perhaps I'm back to square one and need to return my foundation and get the other one. After the experience with the rude and unhelpful salesman the other day I'm not sure he'd even honor his 'maybe' offer to swap them out without charging me another delivery charge.
Obviously I'm finding this quite frustrating. One should lose sleep over buying a bed! Haha.
Thanks so much for your expertise.