I am lucky. I have a dedicated room. I was very impressed by room treatments improving my bass. I have 2-10" subs. I don't think size matters as much as being able to have multiples and treatment. It helps every aspect of the music. I know, this could be a moot point in your case. So if you walk around the room and hear peaks and valleys in bass and you cant do at least one (multiple or treat) try moving sub around.
