Those who have been to Taillevent, Le Grand Vefour and other 2* or higher restaurants in Paris may be better situated to advise cbalaska, but I think that jeans in restaurants of this calibre, even for lunch, would be inappropriate, even if paired with a nice jacket. I don't think you need to be in a dress, or skirt or high heels, but there are comfortable trousers that are a step or two up from jeans that would be appropriate, if paired with a nice jacket or top.