Bob Duggan You won't be able to use embassy letter when you renew next year. You will need either 800,000 THB in an account or pay 25,000 for an "agent" although that route will probably be closed down next.
It's any income not just pension and it's all embassies now as they are unable to do what Immigration wants them to do which is to actually verify your income rather than just regurgitate what you tell them on their letter head which is what has been acceptable up to now.