Hybrid mattress is way too firm, What topper would you advise?

We currently have a super king hybrid mattress which is way too firm.
We want to add a topper as a comfort layer
I’m 6ft and 16 stone (my wife is 5,7 and much lighter) - will the laygel be ok for this size and weight or is the cool blue a better option?
With the current over-firm mattress I get a lot of lower back pain. In any bed I have no one sleep style. I usually start on one side, but will also sleep on my front and back!