This idea met with unanimous criticism.
It came from two streams of thought joining. First, not wanting to spend lots of money on a mattress, and second, being in the market for a camping mattress.
Could both of those be satisfied with a single purchase? Seems like a normal twin mattress is somewhere between $500-1,000, and you can get a fancy thermarest for less than $500.
One of the other appeals of the idea is the space it gains you. If your bed is small and light, it's easy to roll up and put in the closet after you get up, so you get that space back.
This was appealing because I'm about to go from having my own room to sharing a room, and because my piano takes up a considerable amount of space, I was looking for other ways to save on space.
Everyone told me this was a terrible idea. Yes, mattresses are expensive, but sleeping on a camping mattress every night is not worth the trade. The importance of sleep makes it worth it to spend money on something better than a thermarest.
People told me about online mattress companies like Casper or Tuft and Needle that provide basic mattresses, deliver them to you, and will give you a refund if you decide you don't like it within the first 100 days. That eases a lot of the painful parts of buying a mattress for me, so I'll probably do something like that.