We want a firm mattress that will not create a dip for each person even after a few years of use. We are both fairly large and heavy ( 12 stone and 16 stone) and are looking for a 100 percent latex mattress. No springs. Standard UK king. I honestly don't care what it costs - we have had to replace 2 ordinary mattresses in the past 5 year and I'm looking for a really good one.