I'm currently shopping for a new mattress, and I'm getting overwhelmed by the situation.
First of all, I'm 6'2" and around 155lbs (BMI 19.5), my partner is in the same proportions, in our early 30s. I'm a side sleeper (mostly out of habit because of GERD/acid reflux) and she is a "combo", as in really strange positions and quite some movement, although that's not a problem for me (maybe our current mattress is good at preventing movement transfer). I have scoliosis and regular back pain, and have a lot of trouble falling and staying asleep, which leads to bad quality of life overall (tired, headaches, lacking energy, etc.). This started about the same time as when I started sleeping on our current mattress and grew over time, but only realized recently.
We are in need of a new mattress, and we started searching for info and trying out some products at a local store. The first thing we realized is that our current mattress is way too firm.
Do not complicate such a simple thing as buying a mattress. First of all, it should be both convenient for you and your partner. When you lie down on it, feel comfortable, and enjoy being on it, you shouldn't think about other things. When I was looking for outdoor beds for myself, the view was important to me first of all, since it is on the street and all the guests see it, and also the criterion of convenience was essential to me. I've been looking for such outdoor furniture for a long time, but I still did it, and now sometimes I even sleep outside, haha.