Agree with @LoopSki that open water skiing will never be the same. I still free ski, but now whenever I'm free skiing, I'm thinking about working on something to help me run more buoys.
Be prepared for the fact that, depending on your open water technique, running six buoys on a full course is a significant achievement that could seem dang near impossible at first. The mini course is great for helping you see your progress and giving you encouragement as you work towards the full course.
I haven't been to a ski school since college, but they definitely work with all levels. I would probably contact several, tell them about your experience and what you are looking for, and go with whichever one you get the best feeling about from talking to them.