Twin XL Gel Memory Foam Mattress Topper
Dorm mattresses are vinyl stretched over a spring board. Three inches of foam is the highest-impact thing you can add to a room you did not choose, and it rolls up small enough to survive move-out.

You are carrying this down four flights and across a courtyard. Straps, not handles. That is the entire argument, and it becomes obvious in the first week.
Dorm mattresses are vinyl stretched over a spring board. Three inches of foam is the highest-impact thing you can add to a room you did not choose, and it rolls up small enough to survive move-out.
Raising the bed turns dead floor space into the only real storage a dorm gives you. Measure first: most housing contracts cap how high you are allowed to go, and they do check.
These go under the risers. Off-season clothes disappear into them in September and you genuinely forget they exist until the week you need a coat.