For a bunch of reasons I won't go into here, I recently caught the SH-HK, HK-SH T99/T100 train.
Purchased the tix hassle free from the English language booth/counter at the Shanghai Railway Station.
It was a 19-hour journey each way. My husband and I booked a soft-sleeper cabin (RMB 800 each, therefore RMB1600 for the cabin). The beds weren't soft per se but were fine to sleep on. You get your own toilet (which is crucial).
We had our luggage with us in the cabin the entire time (they were large suitcases).
There is also a power point which was a nice bonus (for the laptop).
NOTE: the wankers are allowed to smoke in the train. Technically, they are only allowed to smoke at the 'ends' of each car but it's not like there are windows that can be opened or extra ventilation in place to handle the smoke.
So, if you are booking a soft-sleeper cabin, try to book one in the middle of the car (e.g. cabin number 4, 5 or 6. This helps to control the situation somewhat. I was in cabin No. 5 on the way to HK and the smoke was manageable (I did have to wear a mask here and there at times - strongly recommend bringing along an N100 mask). I was in cabin No. 1 on the way back to SH and it was hopelessly smoked out just about the entire time (in addition to being right next to the end of the car, cabin 1 is also next to a small staff room where I suspect some idiot smoked pretty much the entire journey).
I checked out the next car along which was a 4-bunk per cabin soft sleeper. It looked ok but there was only one shared toilet at the ends of the car!
Needless to say, that toilet was a mess-from-the-seventh-circle-of-hell by the end of the trip. If at all possible, fork over the extra RMB and go the individual cabin with your own loo.