I got rid of my mattress after college. If you are not married/in a relationship, that mattress is going to get ABUSED.
Remember guys, when in college, beds are used for far more things than sleeping.
I'd get something cheap for now. Check out a clearance/outlet place. I got my college bed at a Slumberland outlet center for a few hundred bucks. Not one complaint from either me or my "guests" during those college years.