You're on Niles, aren't you?
If so, I think I know what room you're talking about. I lived on that floor two years ago, and there were two people in it then. One of them told me the next year he found out it was a single, and was pretty upset. There really wasn't that much space at all; being right by the stairwell took some area away I think
You might just have to suck it up; unless you don't want to live with your roommate anymore it'll be extremely difficult to get a new room. Just tough it out and find a spacious apartment next year
Edit: I just reread your post and saw your roommate is moving out. You might be able to get away with not having anyone else try to move in with you, especially if they see how tiny it is. If someone really wants to move in with you just tell them you're gay or something
One of the rooms on Niles had part of an elevator shaft running through it, which made it small as ****. We made fun of that guy.
The stairwell room...isn't that the one where the guy died? I can't remember exactly which room he was in...