Do you have a recommendation for a king size bed that would suit us both?

Him: 10 stone, side or back sleeper
Her: 18 stone, only side sleeper, has lower back problems

We have just returned the Nectar memory foam mattress as it felt like sleeping on a rock and was hard to fall asleep on for both of us, and felt uncomfortable, but in fairness, it was okay for my back support in the morning and helped with my lower back pain. We want something that feels soft and comfortable to sink into, but offers the back support as well. I see your mattresses are recommended firm for a higher body weight - but I'm worried about ordering another mattress that ends up feeling like you're sleeping on a rock!