there is no guarantee that the airline will accept a bus, train or ferry ticket as an onward travel proof. Many airlines insist it has to be a "real" flight ticket
Lufthansa is know as being somewhat strict in ensuring the IATA conformity rules. And keep in mind: If a flight is overbooked, which happens very often, the airline will use the onward-travel proof to sweep out a few passengers. I am not kidding - this is reality, it is insider knowledge
that's why I always recommend to ask the airline by email. You can then print out their email reply and take it to the check-in. On a telephone, people like to talk all kind of nonsense
I know, Thai Immigration in their bad bad English do not make any difference between a visa and a stay permit. . . A few Immigration offices have learned and started to call the "visa extensions" correctly for what they are:
that's a bus that actually crosses the border (many Thai busses do not enter Laos because the steering wheel will be on the wrong side after having crossed)
that's why I always recommend to ask the question by email. You can then print out the email reply and take it to the check-in. On a telephone, people like to talk all kind of nonsense
1. Apply for the single entry 90-days Non-Immigrant O retirement visa in your home country or in any of Thailand's neighbouring countries, before you travel to Thailand.
Prove either that you got the equivalent of 800.000 THB in your home bank account (or in your Thai bank account)
or
that you earn a minimum of equivalent of 65,000 THB per month. For the application to the initial visa in your home country, you can use original income documents.
2. enter Thailand and get stamped in for a 90-days stay permit. The visa itself will expire and become invalid for further use.
3. Visit your local Immigration Office for a Certificate of Residence and the hand out list of requirements to apply for the 1-year Extension of the Stay Permit
4. Visit a bank branch with passport and COR and open a bank account. Transfer a minimum of 800.000 THB to your account. If the banks won’t do it, pay an agent around 5000 THB to open an account for you
You could use the “income method” however that means you need an “affidavit of income” legalized by your embassy in Bangkok as proof of income on Immigration
Some country’s embassies do not issue them any more leaving you with the only option of using the 800K deposit method – at least in the first year.
These countries are AFAIK the USA, UK, AUS, Norway and Canada
5. Wait 60 days and prepare the documents mentioned on the hand out list.
6. As soon as the 800.000 THB have seasoned for 2 months, get the bank statement, visit Immigration and apply for the 1-year Extension of the Stay Permit based on Retirement
You can theoretically do everything by yourself, no agent needed, but it takes certain pressure out of the process if you let an agent handle some parts of the applications
on a 90-days Non-Imm-O family visa, you can fly one-way. You don't need an onward-travel proof. If the Check-in does not comply, ask for the manager and explain to them that this visa is the first step for a longstay in Thailand