Do I need a box spring or foundation?

Box springs are designed to support inner spring mattresses and can change the way a foam mattress feels to some sleepers. We recommend upgrading to a more modern foundation which does not include coils and creates the stable, rigid base that is required for foam mattresses. 

You could also try adding a bunkie board instead of a new foundation as a suitable and wallet-friendly option. A bunkie board is basically a 2-3" board that creates a flat, rigid surface to support your foam mattress and pairs nicely with traditional metal frames, platform beds, and slatted beds.