For dinner one night I would strongly recommend NHOMe on rue de Montpensier in the 1st. Our dinner there is described here.
If you are looking for something more traditional you could consider Chez George on rue du Mail.
There are so many great places in 4th, 6th, 7th and 11th, that it’s impossible to suggest anything without more information. But near the Musée d’Orsay you could try to book a table at Café des Ministères for traditional French, or around the corner at Hémicycle for more contemporary cuisine.
For lunch near the Louvre, I have had several very decent lunches at Café Marly under the arcades of the Louvre. Great interior space too. My husband loves their long skinny croque monsieur. Overpriced but not bad.
