We cannot say enough good things about Nico and his marvelous "Musician's apartment" in Le Marais. The apartment itself is completely charming, very nicely decorated and appointed with everything one would need. The kitchen is small (I wouldn't plan to cook for a large dinner party!) but perfect for breakfast and lunch. The lounge room, separate from the bedroom, is very comfortable with a nice stereo for listening to music. There is also a TV (although we never turned it on--who comes to Paris to watch TV?) The bathroom has a nice, big, bathtub, with a very good shower above.
The location is ideal--easy walking distance from the Châtelet-Les Halles station, which is a direct ride from CDG on the RER B line. The apartment is also pleasant walking distance from many of the important sights and galleries (Louvre, D'Orsay, L'Orangerie, Jardins des Tuileries, and more.) Numerous cafés and restaurants are very nearby and there is a wonderful bakery just around the corner. Major shopping is also within easy walking distance.
I would specifically plan my next visit to Paris around the availability of Nico's apartment.