If you want to apply for an initial Non-O based on retirement inside Thailand, you need to have
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days depending on the local immigration office with your current stamp. It's totally up to how you sort yourself in Thailand quickly if 45 days + 30 days tourism extension is enough or not.
You may or may not try dozens of bank branches to open your bank account while you are on tourist status, the first branch may let you open., etc.
Unfortunately, others' experiences have nothing to do with your application.
You need to go to the local immigration office to get the latest and office-specific requirements handout when you arrive in Thailand.
Here is the 'general' information for in-country Non-O based on retirement for just reference.
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/9.FOR-RETIREMENT-PURPOSES-50-YEARS-OLD-NON-O.pdf
and attached is a rough comparing retirement options.