There currently are a variety of options to travel by night train from Paris (France) to Crest (France), taking between approximately 8 and 9 hours: Namely the INTERCITES DE NUIT n° 5789 and the INTERCITES DE NUIT n° 5787. These lines are operated by SNCF.
In France, a few night train lines are operated by the state-owned SNCF.
SNCF night trains are equipped with standard seating carriages and couchette carriages offered in two comfort classes.
Couchette carriages generally have 4-person compartments in first class and 6-person compartments in second class. The berths are simply designed in both classes and are about 1.9 meters long.
Yes, it's possible to reserve an entire couchette compartment as a private compartment. This can also be done for a group.
First class berths are slightly wider than in second class and there are only four berths per compartment. Advantage of first class: In Paris and Toulouse, there are showers at the stations for first class passengers. In second class, six travelers share each compartment. For cyclists, it's possible to bring a bicycle in second class for an additional fee of 10 euros.
You should bring your own food as there is no restaurant on board. Alternatively, you can pre-order meals and drinks or eat before departure. First class travelers receive a small breakfast. Each passenger receives a night kit with refreshing towelette, dental cleaning tablet, sleep mask, earplugs, and water.