Our bed is very good but feels solid, what would you recommend?

Three years ago we spent ages buying a new bed. We went to so many showrooms and laid on so many beds we lost count. My favorite was the Vispring Sublime Superb, but the price is prohibitive. We eventually bought a Somnus Kensngton 6000 in a medium/firm combination. Although it is a lovely bed, neither my partner (Mr firm) nor me (Ms medium/soft) are completely satisfied with the bed -it feels a bit 'solid' somehow and neither of us sleep particularly well.
I think we would want something springier without it being softer - not sure if this makes sense. We now have th opportunity to buy another bed and move the Somnus to the spare room, and I wondered what you might recommend. One other factor - Ms medium/soft has had a lot of surgery on my spine and have several fused vertebra the the base and some nerve damage in my legas. This results in my back not being very flexible, i.e. if the bed is hard and stiff, my back just fights it as my back will not bend much. The nerve damage in my legs means lying on my side on a hard mattress is very uncomfortable and I spend the whole night tossing and turning.
Any advice would be very much appreciated.