what kind of visa should I apply to stay with my boyfriend who works in China as English teacher?

Hi, I'm Pole, I have a boyfriend in China who is British and working as English teacher. He wants I come to visit him there and stay with him until the end of his contract (which takes 7 to 8 months). Anyone knows what kind of visa should I apply for, if it's tourist visa is it possible to get it for 6 months at least or extend it in China? I saw in the other post that the letter of invitation from my friend is also requied, should it contain any informations about his income as to prove he could afford to support me there?