We flew from Australia with Jetstar on a one-way ticket. No questions were asked. I tell them I'm travelling by land to Laos or Malaysia with no fixed date
I suggest going on book a cheap flight with either Airasia or Vietjet to either Cambodia or Vietnam. (HCMC, Danang or Hanoi have international arrival to Vietnam. from Bangkok, Chaing Mai or Phuket
For immigration the yellow house book and pink ID card mean nothing. The pink ID card can get you some discounts but I haven't seen any. I've been married in Thailand for 5 years,