I have a Hyde and sleep Green kingsize mattress I'm not sure of the firmness rating as it was bought as a present for me by my parents. Initially like others I was happy and my sleep quality improved. However in less than 9 months use the mattress developed a dip where I sleep. I tried to remedy this with regular rotation but it just continues to happen. I am not by any means overweight as a 9 stone 5'6" female and as a busy Mum of three, I spend 6 hours in bed max. I am now suffering with terrible lower back and hip pain which I can only link to this terrible mattress. Reading other reviews I see that this dipping has been a common problem. I would not recommend this mattress to anyone. If you're looking for a new mattress heed the warning and buy another brand.