Start with a 90 days Non-O based on retirement,open a bank account in Thailand,deposit 800k baht and then extend the stay 1 year at the local immigration office.You can then do this annually for 1,900 baht/year. Imo stands for in my opinion. You can always get a health insurance when you're in Thailand. No need for a mandatory one.
You can open a bank account on a 90 days Non-O based on retirement and from there extend the stay for another year as long as you meet the financial requirements. This is by far the most popular method for retirees.
I'm 100% sure you can transfer money to Krungthai Bank. GH Bank = Government Housing Bank is not a business bank,and that might be the reason.There are also payment system upgrades going on,which I guess can affect the possibility to transfer money to some banks,maybe it includes GSB,which imo isn't a business bank.
Still easier via for example KBanks or Bangkok Banks apps if we're talking about regular transfers. And DeeMoney's exchange rate is not better than the TT buy rate.