Hi jcatx03,
Their exchange policy is in post #14 here.
I’m not sure about the warranty … I’ve never asked them … but warranties in general are not nearly as important to me as knowing the materials because the reason most people need to replace a mattress is not a manufacturing defect but the loss of comfort and/or support which is not covered by a warranty. Knowing the materials in a mattress will tell you how long the original qualities of a mattress will last relative to other types of materials.
If your box springs are still in very good condition and have no weak areas or soft spots (you can test this with firm pressure with your knees in all areas) then they would be OK but they will also change the performance, feel, and alignment characteristics of the mattress compared to a rigid non flex foundation. Whether this was better or worse for you would depend on how the total “sleeping system” interacted with you in all your sleeping positions. You could compare the mattress on the box springs to putting it on the floor (which would be similar to a rigid non flex foundation) to see which was best for you but generally (not always) foam mattresses are designed and “rated” for use on a non flex foundation where the foam does the work rather than the box springs underneath.
Phoenix