As a couple, Le Comptoir du Relais works.
A tiny vintage room and a heated terrace on the Carrefour de l'Odéon, where service runs continuously all day — you sit when there's a table, not when a booking says. Lunch and weekends are pure walk-in; only weekday evenings flip to a single ambitious set menu (the one time you book). Charming and personal, but the tables are genuinely cheek-by-jowl.