I LOVE this mattress. I have a bad back - 4 herniated lower discs that are manageable. I'm not contantly in pain or anything, but I do have to be careful not to aggravate the discs and throw my back out. When that happens, it hurts. After doing some research about gel memory foam, I ended up purchasing the firm. I read that the average person typically finds the most comfort from a mattress with a top layer of 3-inch thick / 3.5-4 lb density memory foam & that the best quality memory foam mattresses have a top of layer of 3-inches with a second 3-inch supportive layer. Unless I'm it reading wrong, the description of this product doesn't state the actual density of the firm vs. the medium. The description under "Firm" reads "3-inches of firm gel memory foam" and "3-inches of firm polyurethane foam". Then there's another bullet for "Density" that reads "3-inches of 3.5-pound gel memory foam". I wasn't sure how to interpret that, so I just got the firm thinking that if I ended up purchasing the wrong one, I'd rather the mattress be too too firm than too soft because I didn't want to feel like I was "sinking" into the mattress. I'm pretty sure I made the right decision. I can definitely feel the mattress contouring to my body, but not so much that I struggle to move around & get out of bed. It's defintely firm, but it's a soft firmness if that makes any sense. It's soooo comfortable & I sleep so well on it! I love this mattress so much that I'm considering purchasing the same mattress in a medium for my 11-year old son to see if I can feel any difference. But until then, I am extremely happy with this purchase & would highly recommend it.