Finding the right mattress

I'm struggling to find the right mattress. I am 9 stone and suffer from ME & fibromyalgia. I have been sleeping with a Tempur travel mat on my old Orthosoft mattress (which used to be OK but is now over 10 years old. The Tempur top layer is comfortable but tends to be too warm and both I and my bedroom tend to be on the warm side. I have made 2 mistake buys already this year after trying in a showroom, firstly an Abaca Ramsey medium organic latex - too firm, and now a Myers pocket sprung 1800 medium with natural fillings, but still getting a feeling of too much pressure and find the surface has too many dips & peaks and can feel the buttons despite a blanket and 2 mattress protectors. I am interested in Tempur, but worried about the heat issue, or your equivalent mattress but am a bit concerned about any chemicals used and whether there is off-gassing from the foam.