How do I know which matress is right for me?

I have read through your articles and although very useful information I am now completely overwhelmed and have no idea what I should be buying :(
I used to have (what I thought was) a 100% memory foam mattress and although very comfortable it was always too hot for me. Following a flood my bed was ruined, taking the mattress with it. I was housed in temporary accommodation and given hire furniture. This came with a spring mattress which is cheap - and you can tell. You can feel the springs move beneath you with every turn, even with a mattress topper.
I am not a heavy person - I weight less than 8 stone - and have the bed to myself. I use a king mattress and like a softer feel for comfort (and DETEST the feel of springs under me). I am a light sleeper too (think princess and the pea!).
I need to replace both my bed and mattress and am so confused as to what I should get. Can you help?