Hello.
If you are only going for a month, then this website would be good:-
http://www.homelidays.com/EN-Holidays-R ... RAIN=OLESVI haven't used them to book holiday apartments in France, but for other countries it has worked well. My girlfriend's sister recently rented a flat (as a permanent tenant) in Paris, and French bureaucracy is truly horrific - it was such a major effort to get hold of the property, involving references and every form being filled in three times (its much less paperwork to buy a house in Scotland than to rent in France - which is a bit crazy). Unless you were going to be there for months and months, renting as a permanent tenant probably isn't worth the hassle - unless it was much, much cheaper, that is. She was paying €800 a month, so I can't imagine conventional renting to be significantly cheaper anyway.
It seems every Parisian estate agents has someone who speaks English anyway, if you want to try that route.
Good look anyway. Though it isn't perhaps the most attractive street, rue Daguerre (the nearest metro being Denfert Rochereau) is a personal favourite - it has wonderful butchers, wine merchants, cheese mongers, fishmongers, bakers, and even a rather charming toy and childrens book shop. If you could be anywhere near there, you would be in culinary bliss for the entire stay.
Otherwise, look at Metro maps - being near any station with multiple lines is a major plus.