You can obtain certificate of residence in Phuket from what you outline.
Then possibly a bank account.
That would not work in Bangkok.
You could consider using agent for the bank account. Not expensive.
Yes you can obtain a non O from a visa exempt or tourist visa entry.
Without income letter from your embassy you would need to show 12 months of 65k deposits.
If you don't want to have the 800k in bank you need an agent.
They can do the bank account, non O and extension.