My 15-year old daughter and I had a marvelous time at Antoine's. She counted 101 stairs to the top. The view is incredible, even though Notre Dame isn't lit up any longer. You can even see the Eiffel Tower in the distance, and at dark and on the hour for 5 minutes, it sparkles. The flat has been renovated, with some original beams exposed. It's very cool to stay in an old building like this. On Friday and Saturday night, if you open the windows, you can hear happy sounds of younger people hanging out and enjoying themselves on the Seine riverbank; it's also a joy to see the lit-up boats riding along.
To stay on Isle St. Louis was a marvelous vacation, and the location is excellent, as well as very safe. Many locations are walking distance, and just around the corner are 3-4 corner cafes. This was an amazing time for my daughter's first visit to Paris!