Suki - I bought my bag at Au Bon Marche, it is the only "grand magasin" on the left bank. I shopped there and at Galeries Lafayette (that's my favorite "grand magasin"), they both have little designer "boutiques" within their stores, i.e. Prada, Gucci, Longchamp, Burberry, where leather goods are featured. I think that at both of these stores the leather goods are on the "first" floor (but it's called something else in France, rez de chausee maybe?).
Also one other recommendation - if you like couture and perfume visit the Palais Royale - there is a shop there that sells vintage couture (Didier Malot?) and although the clothes were out of my financial reach the displays were beautiful. While I was there he was featuring an amazing, I think 50's black Dior in his window...wow. Across the courtyard from the vintage clothing store is the Serge Lutens boutique, you may have heard of his perfumes, some are available here but he has an exclusive line that is only available at the boutique (they don't ship to the US). The room itself is beautiful and the salespeople are EXTREMELY friendly. The perfume runs about 95 euros a bottle, not bad at all. To find the Palais Royale, get off the metro stop Palais Royal, across the courtyard will be an official looking building with a French flag flying in front of it, the Palais Royal is to the left of this building - it's sort of hidden behind it.
Have fun!

Thanks so much for those tips. I'm really excited about Didier Malot. I love vintage clothing. I haven't heard of Serge Lutens perfume. I don't think we get it here in Australia.

Do your mean Didier Ludot??

Maybe, someone here mentioned it. I've never heard of it.

suki 7, when we took our daughter in her 20s to Paris, she loved shopping everywhere, but spent the most time in shops in the Marais. However, there are fabulous little shops everywhere and you will just trip over things that are gorgeous. By the way, daughter also works in fashion as a designer. She loved Paris.