Took me over a month to really learn the difference through trial and error, but I made my decision.  I just purchased a queen mattress set, firm, made in a small factory where only 30 mattresses are made daily.   All of them by hand, using coils, cotton batting and just a small amount of foam under the top surface, and they are flippable!  And the real box spring is composed of coils, cotton and wood, not just wood and a cover.  A month ago I originally piurchased a top of the line Symbol Comfortec Firm, with split box (made of wood and fabric only) and had it for 2 weeks and it began to sink in the center.  After complaing to the manufacturer and dealer, I was lucky enough to get my money back which is very unusual.  When I went into THAT store and said I wanted a mattress with NO foam, memorey foam, etc., due to having  had back surgery, and I needed a very frim mattress. I somehow wound up with a foam encased , one sided mattress, about 13 inches high, with about 7 inches of foam on the top.   And I was in pain every morning due due all of that foam.   So, after wising up and constant internet research, I believe that a mattress needs springs/coils for the best support and very little foam, and a box spring that has just that, springs.   So I am well pleased with my soon to be delivered mattress set made of hand turned coils and flippable, and genuine Box Spring foundation.