È possibile utilizzare un materasso come base sotto la struttura del letto con un altro materasso?

To reduce the pressure on back

I don’t think anyone is stopping you but I just don’t understand why??

If you put a mattress directly towards the floor, be mindful of the moisture that builds up under the mattress and does not evaporate because the floor prevents it. You may end up with a mouldy mattress. That’s why the bed frame is essential, or anything that lifts up the mattress off the floor.