Remote Worker could be better, 300 might not be enough but if you could have the employment letter stating your job function and that company allow you to work from Thailand is enough. A cover letter stating your income from company as well as income from pension, along with the 500k THB all in the same account or other accounts as long you explain it in your cover letter supplied with full bank statement no redact.
Beauty of FB, anyone can create any profile having any names so must be careful. When I see so many “I can help” messages… it is expected. Thanks for the warning.
"Letter from company to explain the nature of work in Thailand and allow you to work remotely from Thailand to be sign by authorised person and company’s seal" <- letter must specifically say that.