Hi. we currently sleep on a slatted base bed frame with aSleepeezee 1200 spring with memory foam on top layer which I think was classed as Medium or Medium Firm when we bought it, I at 5' 10" and 15st find this mattress too soft but my wife at 5' 2" and 10 st 11 and a half pound (she insisted I didn't round up) finds it comfortable. My question is would the Fusion 5 be firm enough for me yet soft enough for my wife ? and if it is firm enough will it stay firm enough as the mattress we have has got progressively softer over time making it uncomfortable for me at my 15st weight