Unsure which mattress to go for

Hi , I'm looking for a new mattress and am willing to invest approx £600 -£700 . At the moment my mattress is around 10 years old with a memory foam topper , as you can expect I wake up e dry morning aching everywhere , lower back , neck , shoulders and hips . I don't like a to soft mattress or to firm so I guess I'm looking for a medium , I'm just unsure what to go for , I'm 5ft and weigh 9stone , 5 lbs . There is only me in my bed .