Though not available on most CDG services, the very best class-of-service for meeting the locals and practicing Mandarin (or be an impromptu English teacher) is HARD SLEEPER. On longer distances, hard seat has too many farmers (not to mention an agonizing, sleepless experience) which makes your focus Survival Without Going Insane rather than socializing. Soft sleeper is too enclosed and isolating. I've whiled away many a pre-sleep and post-sleep hour chatting, playing games, etc with ordinary Chinese in hard sleeper. When traveling solo on ZTK/number services, my first choice if I can get it, is always hard sleeper. I do not like to risk being shut in with 2-3 men in soft sleeper, and the lack of air circulation in softs make it uncomfortable for me to get much sleep.

However, I have heard anecdotes for years that for women traveling solo in Deluxe 2-person class, they will try to assign you a cabin to be occupied by another woman when possible...or the carriage staff will reassign you in real-time to be in a woman-share situation or by yourself in one cabin (if a vacancy is available and no woman-shares are possible). I have not soloed on this class of service so cannot vouch for on a first-hand basis.