There is an excellent pizza and pasta place on Rue d'Mabillon in the 6th, just across the street from the marche. REAL Italiano!! A little cramped, but open Sunday night but not Monday. We had pasta and salad and drooled as the pizzas went to other tables. Our pasta and salad were excellent.
Try Santa Lucia, on the rue des Canettes which runs off of Place St. Sulpice toward the Seine in the 6th arrondissement. I am more than a bit of a pizza snob (believing that anything not from around the Golfo di Napoli is almost inevitably not worth having). I thought the pizza at Santa Lucia was every bit as good as anything I've had in the Naples area. Try and stick to the traditional ones: Margherita, or Napolitana (with anchovies -- although In Naples this would be called Romana, but here at Santa Lucia they use the Roman terminology, Napolitana). The Santa Lucia has antipasti, pastas, and a limited selection of meat and fish dishes also. For one week in April I ate 3 times there for a light supper: always having Pizza Napolitana and a mezza caraffa di vino rosso. Deliziosa! The tab - 18 Euros, plus 2 for the waiter. Far and away the cheapest meal I had in Paris that week. Reservations were unnecessary.