What mattress do you advise for two female people both around 9 st 5'5" - currently we have a 2 yr old Myers Ortho pocket sprung with memory foam which I wake very stiff and with sore back and joints. As the mattress is not really that old it isn't that the mattress dips or anything. I'm beginning to read that it may be too hard for our weights? I thought the orthopaedic would be good as I had a road traffic accident and had a number of fractures to my spine. thx