L'Arpege, on rue de Varene, became "mostly vegetarian" a few years ago. It is an expensive, lovely, 3 Michelin starred restaurant that should be able to produce a fabulous meal for an ovo-lacto vegetarian.

typo: rue de Varenne
It's on edge of 6th and 7th arr.

You might want to think about renting an apartment. Some of the many sites allow by the night - my sister and I rented one in July for three nights. That way you would be able to control at least a few meals per day by shopping at the many open air markets and preparing your own meals and then just going out to the different restaurants that have been recommended.

I was going to mention Arpege! But since this is in the top-rank price-wise, it might be out of reach for the OPs budget..and would need to be booked ahead..

http://www.alain-passard.com/fr/



I did have a good lunch at L'As du Falafel on Rue des Rosiers..a Sephardic place; not sure if this is vegan or not but is is a fun place with decent food. the menu extends beyond falafel; they also do non-veg dishes.

This is the most famous, but there are other falafel places on the street that I have not tried...