We stayed in Catherine's apartment for 6 nights and had a wonderful time in this perfectly located space. So close to the metro, river, Notre-Dame, and the Saint Germain restaurants that it is easy to go off in any direction and get anywhere quickly. At the same time, it is so quiet and peaceful. We were a little worried when we arrived since there is a building renovation going on across the street, but nobody ever seemed to be working so we did not hear a thing. Even though Catherine provided us with a whole list of restaurants to eat at, we actually spent a few nights having a bottle of wine and our meals sitting in her living room with the great big windows open to the tree outside. That is how peaceful we felt. Her kitchen is very well stocked and we used the French Press coffee maker every day. The bed was very comfortable and you can close the shade on the slanted window above the bed to make it dark. Catherine was not able to meet us on arrival but left a key in a safe place for us and reached out several times to ensure we arrived OK and to check and see how we were doing throughout or stay. Her communication was excellent!
A few slight issues to be aware of: The flat is on the 5th floor (American), 4th floor (European) so if you have any heart or mobility issues, the climb will be tough. You need to sit down in the tub to take a shower, but I think this might be common among French apartments so maybe it is a spoiled American issue of mine :) And lastly, this is Catherine's actual apartment with all of her clothes and decorations and books, books, books, which is what provides the charm of being in a wonderful Paris flat, but is not for everyone that might want a more sterile hotel like setting.
Aside from those small caveats, I would highly recommend this place, especially if you want to really feel like you are a Parisian!