You really just need to get a QR code generated when you fill in the form to show at immigration. Saw a video on line that said the form currently accepts the departure date being left blank.
We too are travelling in late August and personally I will check then if a QR code can be generated leaving the departure field blank. If not, we’ll book tickets for less than $20 each on the onwardtravel.com travel website.
I get the requirements as laid out above and plan to retire in Thailand with my wife. Presumably she must also follow the 800k - 65k procedure with her own bank account?