Oh my god, I feel so stupid. I don't know why I read duvet, not mattress. That's funny though.

My Ikea mattress came rolled up very small. Not quite suitcase-sized, but if you find a way to get close to such a size using simple tools (something you can fit in a backpack or carry-on), I can see this happening. One wouldn't need a human-size suitcase to pull that off.

Note that this is based on mental estimations of a ten year old memory. I may be off about how small it was, but I think the estimation should be accurate in essence.

Some mattresses can be rolled. At least IKEA sells them that way.

https://www.youtube.com/watch?v=8DQlKDSvK7M

Hotels should be suspicious of guests with extremely enormous luggage.