Apologies in advance if this gets a little too detailed!
We are just about to buy a new pocket sprung mattress. My wife is 5' and approx 8 stone 7lb, I'm 5'11" and 12 Stone 10lb. I was/am a little dubious about dual tension mattresses, especially ones that you can't turn. I think however that yours are all turn mattresses? Looking at your charts, our combination of weights and sizes perhaps put us on the borderline. We do both have sporadic lower back issues, but do not like firm mattresses. I sleep on my side and my wife on her back and sometimes on her front, which sometimes causes some of her aches through arching. I think she perhaps needs soft tension and me medium. However, I'm a little unsure with the large range you have, which to go for. Of the beds we've laid on in shops recently, I quite like the feel of a Marquis & Moore (Wessex) medium seasonal turn mattress. Not sure if you will have heard of them (I think Harrison actually make them), but maybe you could advise me on a John Ryan equivalent?