sound like you want to 12 month extension of stay. you need 800k Baht in a thai bank. If u have problems getting it use a visa agent to help. You might want to start getting up to speed with Thai income tax. This vid might help u.
"even if Thailand changes its laws to tax worldwide income, it doesn't mean that EU countries or any other will suddenly start handing over your data." wrong, They have been "handing over data since 1024. "No country is going to just hand over tax returns or personal financial details." wrong, they can access everything, but if you want to claim DTA them you must provide proof that you actually paid tax in the source country, so you will be handing over tax return and receipt for payment otherwise your DTA claim will be denied. Read the last page remarks.