ACCOMMODATION
My recommendation is that you choose a hotel nearby a connection with RER B network. Orsay is about 35 mins by public transportation from station “Denfert-Rochereau” (Paris 14). If you join for dinner it's also much more convenient to stay in a hotel in the city centre.
See maps on http://www.ratp.fr/plan-interactif/
Suggestion of hotels close to Jardin du Luxembourg:
Hotel Novanox *** Bd du Montparnasse - 2 mins to RER B station Port Royal http://www.novanoxhotelparis.com/
Hotel Observatoire Luxembourg *** 107 Bld Saint Germain - 1 min to RER B station Luxembourg http://www.observatoirehotel.com/en/
Hotel de Mines ** 125 Bld Saint Michel - 2 mins to RER B station Luxembourg http://www.hotel-desmines-paris.com
Suggestion of hotels in Quartier Latin
Minerve hotel *** 13 Rue des Ecoles - 10 mins to RER B http://www.parishotelminerve.com/
Hotel Quartier Latin *** 9 Rue des Ecoles - 10 mins to RER B station St Michel Notre Dame http://www.hotelquartierlatin.com/fr/
Hotel Sully Saint Germain ***, 31 Rue des Ecoles - 10 mins to RER B station St Michel Notre Dame http://sully.latinquarterparishotel.com/
Hotel Moderne Saint Germain ****, 33 Rue des Ecoles - 10 mins to RER B station St Michel Notre Dame http://hotel-paris-stgermain.com/
Hotel Californa Saint Germain ***, 32 Rue des Ecoles - 10 mins to RER B station St Michel Notre Dame http://www.france-hotel-guide.com/en/75005-hotel-california-saint-germain.php
Villa Pantheon, 41 Rue des Ecoles ****, 41 Rue des Ecoles - 10 mins to RER B station St Michel Notre Dame http://www.villa-pantheon.com/fr/page/hotel-villa-pantheon-accueil.50.html
Best Western la Tour-Notre-Dame ***, 20 Rue Sommerard - 5 mins to RER B station St Michel Notre Dame https://www.bestwestern.com/content/best-western/en_US/booking-path/hotel-details.93611.html?propertyCode=93611
Best Western Le Jardin de Cluny ***, 9 Rue sommerard - 5 mins to RER B station St Michel Notre Dame http://www.hoteljardindecluny.com/en/
More for city centre
Many offers for accommodation on the official website "Paris Tourism Office"
http://en.parisinfo.com/where-to-sleep-in-paris
Other useful link:
All tourism Information on http://en.parisinfo.com/
Close to IPN:
Hotel d'Orsay
2 rue François Leroux
91400 Orsay
http://www.hotel-orsay.com/
RER B station : le Guichet (from Paris, one station before Orsay-Ville)
5 minutes by walk from the station
and
15 minutes by walk from the IPN Orsay (map)
Hotel Le Village
4 rue Neuve
91190 Gif-sur-Yvette
http://www.hotellevillage.fr/
RER B station : Gif-sur Yvette (from Paris, 3 stations after Orsay-Ville)
