I can definitely recommend Peter's apartment. It is conveniently located in the heart of St. Germain, only a few steps away from the Louvre, the Musée d'Orsay and the Boulevard St. Germain.
I stayed here with my girlfriend and we really enjoyed our time. It is really quiet and cosy but still in the very heart of Paris. The apartment was very clean when we arrived and Peter is a really nice host who is really easy to communicate with.
I would really come back when next time in Paris!
Thank you