We had a fantastic stay at Lalé apartment.
First of all the kindness of Lalé is superb. He give us lots of recomendations about Paris and communication with her before arriving and during our stay was very fluid.
Regarding the apartment, it is located quite in the center of Paris, with a 20-25 minutes walk to Notre Dame for example (it usually takes more because all the interesting things until reaching there!)
There are several metro and bus lines in a 3 minutes walk ratio from the apartment that will take to anyware in Paris.
The apartment itself has the pros and cons of a XIX (or even late XVIII I don't know) century building can have. It is old and charming. It has an elevator, but it starts from the first floor, so there are several stairs to it. We were carrying a big suitcase with us and it would have been better if the elevator started from the ground level, but wasn't big deal anyway. It is also narrow for just 3 people due to the original available stairwell but far better than nothing.
On the other side the apartment is quite big with a sunny living room (even on usual Paris cloudy days there is a lot of light in it) and a quite big bedroom.
Don't expect a fully modern renovated apartment. It is as warm as a home can be with creacky real oak wood floor and furnitures and decorations being added during several years, just as the pictures show.