Your 2nd post, OP, sounded like you came up with the right attitude. If, however, you still feel the same way you expressed in your 1st post, please reconsider.
I'm not much older than you are and I have a full bust too, so I know where you're coming from. My supervisor and other co-workers are 30-45 years older than me. They dress very differently from how I do. What they consider too revealing isn't to me. As much as I hate it, for the sake of getting along and not getting terminated, I have to follow the same rules as everyone else and wear the same dowdy clothes they do.
Unless you have a huge trust fund coming your way or will win the lottery or something like that, you'll probably have to work to earn a living. Even if this is just a side job for you while you're going to school, this job is still part of your work history, and it's a good chance for you to get practice in customer service/people skills. Even if you decide to go into higher education and get an advanced degree, your workplace will have a dress code. In fact, you'll likely be held to an even stricter standard if you end up in a higher position.
I agree with the other posters that your co-worker was polite in explaining to you about the dress code. If all you have to do change in order to keep your job and get good reviews is put on a cami or wear different-style shirts, that's nothing.
I had to buy a whole wardrobe in order to conform to my company's dress code, but for those clothes, I bought from the 75% off rack at Macy's and went to Old Navy. I recommend you do the same if you have nothing appropriate right now. The clothes will also last a long time if you'll wear them only at work.