if you are on visa exempt, you go into your local immigration office with: a printout of proof you are staying at your current hotel, a passport photo, a copy of your passport main page and the one with your Thailand stamp, your actual passport, a pen to fill out the official extension form since the ones in the office probably won't work, 1900 baht, some patience... worked fine for me, my wife, and 5 year old son last week in Chiang Rai. Chiang Rai immigration is at the mall, so good to get lunch, and has an indoor playground for kids, so all good!
Thailand has tax credits, and a graduated income tax rate, so the actual tax amount on 28k won’t be too high. That is a spectacularly small income for an expat from a western country, and he certainly doesn’t need to worry about taxes. Any difference is small and more than made up for by cheaper living in Thailand.
Australia tax rates are just as high if not higher than Thailand, is that what you are bragging about? And no, you don’t get to pick whether or not you are a tax resident of Thailand. It is possible you may not owe any more taxes in Thailand, but you will still need to file.
ffs no, you are almost completely wrong on every aspect. You are a tax resident of Thailand if you meet the criteria, and you don’t seem to understand how DTAs work.