When I stayed here, the Relais Christine seemed to be among the best of the Left Bank boutique hotels. Still, remember that it's a small boutique hotel (with excellent and personal service) that doesn't have the range of facilities and services that one would expect it an palace hotel. IIRC it's also relatively close to an RER station if one plans to use public transportation to/from CDG (with no transfer required, so fairly easy to do with some luggage).