We took the overnight train from Hangzhou to Changsha. We booked soft sleepers, which are four beds to a compartment. Reasonably comfortable (free slippers!), but there were actually three other occupants, one of whom was about 12 months old and did not exactly sleep soundly through the night. However, perhaps a small child is better than alternatives since it seems you can smoke on sleeper trains. Almost every other compartment in our car was thick with smoke.