On the night trains in France, the so-called "Intercités de nuit", you have three comfort classes: reclining seats, 6 berth sleepers and 4 berth sleepers.
The railway company SNCF is advertising with a possibility to book privative compartments ("espaces privatifs"). This means that if you are alone or in couple, you can have a whole compartment for yourself, by paying a supplement.
However, when I try to book a trip online I can't see this option. I can only see an option for single female travelers. That's not of great use to me. Thus, could someone please explain me how to book this privative compartments online?
P.S. I know that it is possible to book four or six persons in one compartment and only effectively use one or two places. That will be very expensive. I am not interested in this option.