I think you should wear a suit. You can go with a shirt underneath the jacket. If it makes you comfortable, you can certainly unbutton the jacket (or even take it off) when you sit down. Did the school specify dress code? If they said business attair, then definitely you need to wear a suit. I've been to an interview where the instruction says business casual, and when I got there, everyone is in black or dark gray suits! Definitely glad I didn't go on the casual side.
oh my god, I always thought cranberry is a mm! glad I didn't suggest a jacket with matching skirt Now that I finally got that straight, yeah, I think you can go with a shirt.