7 stones and looking for a firm bed with a soft top layer

Hi,
My husband and I are both light weight - I'm 5 foot 2 and 7 stones and my husband is 5 foot 7 and 8 stones.
Having grown up in China sleeping on hard surfaces we find soft beds very uncomfortable. But we also love the top layer to be soft (back home we tuck quilts under the body when we sleep).
Over the last 10 years in the UK we've always preferred memory foam to sprung mattresses because they're soft on shoulders and hip bones but provide adequate support. There have been occasions where we had to sleep on the floor in a rented property because the soft mattress was giving us back pains.
However lately I've developed a problem with heat such that moderate warm temperature (above 21 degrees) would give me a headache. We have turned the heating off in the bedroom permanently but the memory foam mattress still gets too hot in the coldest of days.
We've just bought a house and looking to invest in a good mattress and that's why're here.
Could you please help us find one?