I have had some wonderful times at this little bistro. Bistrot Vivienne is at 4 Rue des Petits Champs, just north of the Jardin du Palais Royal. It sits at the end, and inside of a lovely little shopping mall called Gallerie Vivienne. You can eat inside, which is pretty cozy, and there are great tables in the Gallerie. If the weather is good, you can also sit out the front like a Parisienne.
They do a really good authentic Crème brûlée. It’s not cheap, about €25 for a main. The Magret de canard (duck breast) is good if you can cope with the concept of fois gras (this is Paris, after all). It’s also good for cocktails.
Wheelchair access is fine, and it’s best to book ahead.