We went to a pocket sprung memory foam mattress last year.
Only just getting used to it now.
1300 pocket springs in foam, 10" thick with a Two & a half inch memory foam topper sewn in.
Nice and firm, without being hard.
We had previous a waterbed so it has taken a lot of getting used to.
Try these peeps. Land of Beds.co.UK
We had very good service from them and at the time best price. (but always search for a better deal)
This one is the nearest spec to what we have, as beds are constantly changing spec.
http://www.landofbeds.co.uk/hypnos/mattresses/orthocare-visco-1200/king-sizeRay
PS. We were told at the time, (FWIW) if you go for more than 1300 springs your wasting your money.