It sounds like a Non-O Retirement Visa (for over 50s) is the Visa that best suits your requirements as it will give you 90 days on entry (single entry)
if these are seasoning requirements you need to state which Embassy or Consulate has the application requirement and which Immigration Office has the extension requirement
If you don't already have a Thai bank account open one during your 10 day stay and transfer the 800k so that when you return the funds will be seasoning ready for your first 12 month Extension of Stay (assuming that your Embassy does not provide the income affidavit).