We had an absolutely wonderful stay at Catherine's Apartment. It was fantastic.
Catherine met us at the beginning of the stay to give us a tour and to show us how everything worked (like the TV, the key, the dishwasher, and the washing machine). She told us about the area and suggested nice places to eat near the apartment. She even checked in with us a couple of times throughout the stay to see if everything was going smoothly.
The apartment was on the second floor (two easy sets of stairs to navigate), and it in the heart of St. Germain. It had everything we needed for a great stay. Strong wi-fi, a large fridge, cook-top/stove, electric kettle, comfy bed, shower with great water pressure and lots of hot water, and an easy to operate TV with a variety of French channels, and a nice fan for the occasional hot night.
The location was spectacular. There was a Carrefour around the corner for groceries and beverages, a boulangerie even closer where we would buy our daily "baguette tradition" and the occasional dessert or croissant. A Michelin star ramen restaurant very close, and dozens of cafes and restaurants and shops all within a couple blocks. There is a movie theater just up the street (as well as a convenient metro stop at Odeon). We had the Navigo cards, and didn't need to use them often. The apartment was easy walking distance to just about every attraction we wanted to go to including the Louvre, Musee Orsay, cooking classes in the Marias, and Luxembourg Gardens.
Easily the nicest apartment that we stayed at in Paris, and highly recommended.