Just thought I'd add to what other people have been using in China.
The app and website for www.writtenchinese.com/ have proved very good with some great extras for a few quid. As for one on one teaching I've been using www.italki.com lately, this site sets you up with a qualified teacher of your choice to learn one 2 one via skype. Lessons can be set at your discretion and the teachers have varying prices so it's good to find a bargain (you get to have three trial lessons with different teachers you choose). Good way of getting that important Chinese one to one learning.
As for changing tourist visa to student visa, I can't see why it's not possible but don't quote me 100% on that I'm afraid!