Something with 1200+ springs in should help.. Haven’t you a John Lewis near by you could bounce on a few there, like I did last week.
I ended up getting JL’s own branded mattress with 1200 springs in, so far I’ve slept in it 3 times and the first night was very odd and disturbed, 2nd night much better and last night the best nights sleep I’ve had in sometime.
My old mattress was only 5 years old, again bought from JL, but I chose a thinner mattress and a top thingy that was about 2″ thick, once that had squished down (filled with down) it was just a couple of trenches on the mattress, so I got shot of both.
Good mattresses can be mighty expensive, upwards of £1200 if you want some fangled thingy, but mine was £699 and I think that’s quite a lot of moolah, but hey..
It’s quite firm, but I’m going to get an 1″ topper thingy on it to soften it up a bit.
HTH