Best mattress for tall guy

Husband is 6ft 6 inches and a insomniac - we need a big bed that accommodates both of us, however he likes a very firm mattress ( he is around 14.5 stone) and I like it slightly softer ( 11stone and 5ft 4 inches) He gets very hot so therefore wants a mattress that keeps him cool or a fabric that doesn't increase his body temperature! Help, we've been looking for awhile!