instead of spending money on a base you might not use after buying a bed why don't you just place a clean sheet or a rug under the mattress for the time being?

alternatively look for a used futon frame on craigslist. that's whats underneath our mattress for now (but shhhh - during smallest-coolest someone was impressed we didn't have any futons!)

We've been sleeping with our mattress on wooden bent slats (ours are from EQ3) that sit on our floor for several months. We had designed a bed to be custom built that would incorporate the slats, but we lost our woodworker so we'll probably be on the floor a while longer. Personally, I don't think that there's much of a difference between slats and bare carpet, but I'm a lightweight who doesn't stress the mattress coils very much.

Slats work fine for me, but you should turn you matress once in a while so it can "breathe". That would also be my point against placing a matress directly on the carpet, you simply risk mildew due to lack of air circulation.

dito what pluspuls said. mattress on the ground equals mold.

If that slatted base is rigid (the one in the picture doesn't look like it, but some have metal U-channels over the length) they can be supported with 4 small blocks, thus providing a lot more ventilation.

you'd have to make sure the dimensions would work, but what about placing the slatted base on the bed frame you can get for free when you buy the mattress? i have a platform bed with a slatted platform that lifts up for storage, so it's a basically the same thing and works rather well. would get it off the floor, etc.