busy at BKK yesterday when our flight arrived ~30 minutes early around 08:30. So not sure if the issue was Immigration or with the arrival coinciding with that of others. Some vacant Immigration booths and a fair few Indian sorts queuing too.
If you’re intending to go to Vietnam and Laos anyway, why not apply for a Non-O when there. Can get advice as to what might be quickest? On return to Thailand on a Non-O, open a bank account and deposit your funds. Retirement is a simpler process than Marriage provided you have the funds.