Wear what you are comfortable in. It's not a job interview, and you will not be judged on your appearance. On the other hand, you will make a good impression if you appear clean, tidy, smart and organised.
I really wouldn't worry too much, people going for university interviews wear anything from suits to full goth regalia!! As long as you feel comfortable and confident you will be able to represent yourself well.
Your outfit sounds fine, good luck! Hope it goes really well for you. As you say, if you feel comfy it will work. Have a couple of good questions of your own to ask at the end, it helps to make you feel it's more of a dialogue than an interview. Enjoy it!