Here are links to a few mostly 2-star hotels that may "fit the bill." Linda has mentioned Le Clement, which is well regarded here, and elsewhere. We know and like the Hotel Monge, and our favorite is the Hotel de l'Avre which is a bit out of the way for your requirements, but has good bus and metro access.

Of course, I'm not aware of your budget parameters, though you did mention 3-star. but we seek out the best budget accommodation we can find and use the money saved on hotels to either extend our stay, or to hasten the arrival of that glorious day when we are off on our next trip!

These hotels cited below all get good reviews on tripadvisor.com, with the Grand Hotel Saint Michel, a 3-star, receiving the most "mixed" evaluations and also being the most expensive.

Grand Hotel des Balcons 3, rue Casimir Delavigne (6th) 180 euro triple http://balcons.parishotels.it/

Hotel Le Clement 6, Rue Clement, (6th) 145 euro triple http://www.clement-moliere-paris-hotel.com/

Hotel Monge (5th) 125 euro triple Rue Monge http://www.hotelmonge.com/

Grand Hotel Saint Michel (5th) 210 euro for family room http://www.grand-hotel-st-michel.com/

Hôtel de l'Avre 21 Rue de l'Avre (15th) 110 euro triple http://www.hoteldelavre.com/

Good luck, and have a wonderful time!

Kevin in Fredericton, NB