I found some very lovely fabric in BHV. I covered a bench with it and it always reminds me of Paris. I also bought an open and closed sign in french for my fireplace. That was a cool find. We ate at the cafeteria on the top floor. Very nice and reasonable.
Across from Bon Marche is their food store. We bought a picnic dinner there and took it to the dock of the Seine river cruise and ate while we waited for dusk to take the cruise. It was memorable. Enjoy!

I don't recall anyone's mentioning the GL in Montparnasse, quite a nice smaller store.