A few years ago, I purchased a spare single mattress from IKEA Rhodes and carried it home on the train. It was awkward trying to fit that into the train vestibule. It was even more awkward trying to lug it to the station in the first place. So I for one am stupidly grateful that IKEA is now selling a range of mattresses in a rolled-up format instead.
Most people don't take large items of furniture on trains, but a rolled-up mattress also has a better chance of fitting in the boot of a car or back of a 4WD. The obvious trade-off is that these are likely to be mattresses you keep as spares for visitors: any mattress you can roll up is going to be less comfortable than its spring-filled full-time equivalent.