I am happy with this purchase! I really had a hard time deciding whether I wanted it in "firm" or "medium". I generally like a really firm bed and need it for my back, but the reviews convinced me to go with the "medium" firmness. I have no idea if there is really any difference between the different levels of firmness or if it's just a marketing strategy, would love to see a review from someone who has bought 2 in different firmness levels, but anyway, the medium is firm enough and I am very happy with it. Like other reviewers say, you don't sink way down into this mattress, you sink a little and the heavier you are the more you will notice. I am 5'9 and weigh 150 and it sinks very little (which is good). I feel like I am getting really good support for my back, without the feeling of being on a really hard mattress, like I was with a traditional spring mattress.