I recommend staying at Julien's apartment. We had everything we needed to have an enjoyable week in Paris. 3 minutes walking to the metro, 9 minutes walking to the Gare Montparnasse, just 3 minutes walking to the Casino supermarket.
And the most important: it's a lovely place! good shower and beds, no noise from the streets.
Julien is an easygoing person and always gave us a quick answer to our doubts.
We had a great week in Paris!