With China Southern, you can select your own seats on their own website once you have the 16 digital eticket number.

It gets a bit tricky in the fact that you beed to be a member of China Southern Airlines to do it. Just join skypearl and from there, once logged into the website, click online services and then seat select. You'll then add the eticket number and name. That's it select your seat or pick special meals.