The best memory foam are tempur. Been using one for over 8 years.

They do a 100 nights money back guarantee.

They are expensive, but you can pick up at a good discount at their outlet shop in Wembley. They deliver to sw12.

We've got the cheapest vi sprung mattress from John Lewis, I think it was £999, it's on wooden slats too. It's extremely comfortable, we sleep really well on it.