I love memory foam mattresses and wouldn't want to swap to sprung, but I spend a lot of time sitting on the edge of my bed - so my mattress develops a slope/flat bit over time. I spend around £300 on each mattress bit could I avoid this problem if I spent more on a mattress, or bought a different type?
My mattress is a tempur which is arm and a leg time. I too sit on the edge of the bed in the same place. My mattress is now 9 years old and looks like new. The only thing I can think of is that my bed base is the kind that has solid wood slates and an edge all round so it sits in a shallow box. The box isn't high enough to cut in when you sit on the bed but it supports the sides.
I hate sprung AND memory foam mattresses. There is an alternative...proper latex (for example, Dunlopillo). I've never slept on anything else....apart from when away from home.