Chantilly The Centre has excellent library of 600,000 volumes.
Many scholars stay there in the summer months.
I have had several research stints in Lille. Most trips, I stayed with a family, but I stayed at an apartment hotel the last time I was there. The hotel in Lille is well located, close to the train station and the metro, which makes the archives easily accessible. It is also close to the TGV, grocery store and the old quarter. It is, however, not cheap, but at least you can cook for yourself.