You might as well sleep on the floor. If it was five inches,when you sit on it, it's like sitting on the floor. I doubt anyone would be able to sleep a night on this thing. If there was wrapping to send it back I would. Very disappointed. There is nothing,absolutely nothing plush about this.
I was very excited to order this item because the price was great. Unfortunately, when I received the mattress it was barely 2 inches thick. I think part of the problem was how it was shipped. It was folded in half and rolled up which no doubt caused the padding to be reduced to nothing. I wish I hadn't thrown out the old mattress because even at 15 years old it was still better than this one. I would have returned this in a heartbeat if I hadn't thrown the other one out!
I was led to believe, by the one-star reviews on various sites, that this mattress would be as hard as a rock. That's what i wanted! Instead, i find that it's not actually dense, it's just very thin, so how "hard" it is depends on what is beneath it. It could also use some ties to hold it in place when i fold my futon up into a couch or down into a bed. I think if i put something denser beneath it, it will feel as firm as i wanted. It looks nice, arrived quickly, and was exactly as advertised, so not bad (especially for the price).