I Only Weigh 50kgs

Help, I bought a Soft Tension Vi Spring 'Coronet' mattress, and matching base, nearly two years ago. Owing to my lack of weight, and, very thin build, I found it too firm, so, added a latex topper (from Latex sense). This has helped, somewhat, but is still not giving me any comfort, and, I'm still getting sore pressure points.
I must add, I suffer from osteoporosis, and, chronic Fibromyalgia, so, pretty much every mattress I've tried feels too firm. In my mind, I feel that I need a very soft tension mattress, with, a lots of soft, upholstery, which won't flatten in a fairly short period, which the VS Coronet has, despite my lack of weight, and, as mentioned, very thin build. I appreciate this is a lot to ask, but, would really appreciate your help, as I'm getting, almost, desperate for a comfortable nights sleep.
Many thanks, in advance.