Second class sleeping cars have 3 beds in each compartment and first class have 2 beds. Sleeping cars are usually unisex, which means you and your wife will have to sleep in separate compartments (although if you take a first class one you might be able to share it).

The beds in the sleeping car are much wider than the couchettes, and they have 'real' mattresses, sheets and pillows. There's a sink in the compartment for washing, and each passenger gets a towel, soap and drinking water. There's a lot more room and it's much more comfortable than couchettes.

Laurie in Mexico City