I did it twice so you don't have to. I put a layer of 36 on top and a layer of lux on the bottom. It wasn't firm enough so I did it over with all lux. It always gets a little softer from use so if it feels too firm at first, it will soften up some. I think I used their high quality stuff to get a longer life out of it. Cheapest way to buy it is to order it in a mattress size and then cut it to the dimensions you need. An electric carving knife is amazingly great for this task. Walmart has one that's less than $20.