We stayed at Christine's apartment for 12 days. It was a fabulous location, walking distance to the Louvre, Eiffel Tower, Notre Dame, Concorde and the Metro. I highly recommend Saint Germaine, 6th arrondissement.
Our flight arrived early and Christine found a cafe we could leave our luggage while we walked around until we could check in.
It was clean and perfectly quiet at night even though it is close to bustling streets filled with cafes.
The bedroom is rather hot, as it is a loft with no air conditioning, but has a skylight that we left open to help ventilate the room.
Also be prepared to carry your luggage up the four flights of stairs. This is to be expected though in Paris due to the era of the buildings.
Overall a great apartment that served us well.