You can take the Elipsos Trenhotel directly from Barcelona Franca to Paris Austerlitz, leaving at 21:05 and arriving at 09:00. You can get a discount fare by booking well in advance at the Spanish version of www.voyages-sncf.com and choosing to pick up your ticket at a station in Spain. But a man and a woman traveling together will need to book a double cabin. Couchettes are same sex only on this train.
A cheaper option would be to buy a ticket in Barcelona for Barcelona Sants-Cerbere, leaving at 17:25 and arriving at 20:07. Then if you can handle French, book the Cerbere-Paris Austerlitz night train, leaving at 21:21 and arriving at 07:27, at www.voyages-sncf.com well in advance to get PREM'S fares: 35€ for a bunk in a six-person couchette or 60€ for a bunk in a four-person couchette (worth it for the extra space and comfort). Men and women can share these couchettes. Leave France as the default country, do NOT choose cancellation insurance and print your own ticket at home.