Go to LINTOX 11 rue Lepic, metro Blanche near the Moulin Rouge. Large selection. The owner is pleasant and you can try on at your leisure. A regular haunt of mine when in Paris.
Also, Green Village 17 rue de la Verrerie in the Marais, near the Bazaar Hotel de Ville departmental store. Metro Hotel de Ville. Not such a wide selection as Lintox, and I do not think they allow you to try on.
Happy shopping!