Which mattress would provide comfort taken my weight and height

I need a new mattress to use with my sprung divan base. Most mattresses I have come across are too hard for me. I acquired a medium/soft memory foam mattress a few years ago from a manufacturer who asked some very pertinent questions regarding my weight and height and other relevant issues. As a result, the mattress I got was very comfortable. The manufacturer seems to have gone out of business, however, and I am experiencing difficulty finding anyone else who can advise me properly. I am not wedded to the idea of memory foam, incidentally - I just want a mattress which is comfortable .
I am 5' 9" tall and weigh a smidge under 10 stone - i.e. my weight is spread across a fairly large surface area so I don't really sink in that much. I was hoping to pay around £400-£600 for a standard double (4'6") mattress.
Perhaps you could advise whether you have something suitable for me.
Thank you.
Helen Hardman