Ideally a proper foundation is one that is sold to match the mattress. The mattress and foundation work together, acting as a unified shock absorber.
It is OK to put a mattress on a solid platform bed.
We recommend against putting a new mattress on an old foundation. Using an old foundation with a new mattress will jeopardize the new mattress.
Even if the foundation looks new, a new mattress will soon sink into the areas where an old foundation has been worn. Putting a new mattress on an old foundation may also void your warranty.