@Yaoyu **********
I told you, the ONLY extension you can get is the 1-year extension. There is no other extension available to you. After that you will need to leave Thailand.
You can try returning on visa exempt and see if your immigration office will allow you to apply for a new non-O visa in Thailand. Some offices allow this. It will require a few extra trips to immigration though.
First you apply for the non-O Visa, then you get an "under consideration" stamp with a date to return. You return on that date and get the non-O visa in your passport. Then you wait until 30 days before that time is up and go to apply for your 1-year extension.