Sleeps hot, poor edge support

We have tried different toppers and sheets (most notably cotton percale, which was cool on our previous mattress) to no avail: the mattress sleeps hot. It also develops depressions over time and the edge support is terrible. We initially tried to return this mattress and were offered an exchange instead. We asked if we would be able to try out the exchange, which the company confirmed and they said they would extend the trial. Unfortunately the exchange slept even hotter and they denied us the return.