In the 6th not 7th, but you might find the Hotel Ferrandi to be suitable.
The Ferrandi is a small (30-40 rooms), low-key, 3* place on a quiet but interesting street (art galleries, tea shops, etc) between the Montparnasse tower and the Bon Marche department store near St Germain des Pres. The rooms I've seen are ok-size for Paris, though bathrooms can be small.