Many people have suggested one of the onward ticket sites. Just be aware that every onward ticketing site only makes an on-hold reservation that shows as pending, not an actual paid ticket with an e-ticket number. This means there is always a chance that a knowledgeable person reviewing your proof of onward travel will know it isn't a valid ticket and is nothing more than a hold. You could actually do the same thing yourself by booking a flight on any airline website that allows a ticket hold for a few days or that allows a ticket hold to pay at the counter or at a store. It would generate the same reservation with a valid PNR booking code pending your payment. If you are using it at an airline check-in counter when they ask for an onward ticket, the check-in staff usually knows to look for an actual e-ticket number as PNR codes don't indicate it is an actual ticket. Onward ticket sites work well when applying for visas where consulate officers typically don't know the difference, but it is risky using it at an airport check-in counter when you have a one way ticket.

Printed. They take a scan of it at immigration. Using a phone makes it much harder for the immigration officer.

@Brandon ***********

Samui requires it to issue the residence certificate, based on what was required when it was needed to get the temporary licence.

@Stuart **********

thanks, I'll see if anyone else can confirm this personally.

OK folks, for all of you answering, I can tell many of you don't know what an eSIM is, and are answering for old fashioned physical SIM cards. Please look up eSIMs as it is not the same thing. New high end phones support eSIMs where you download a virtual SIM rather than change physical SIM cards. Some phones like iPhone 14s and 15s sold in the USA don't even have physical SIM card slots any more and require you use eSIM.

@Ivan ********

you must not know what an eSIM is eSIM is not a physical SIM card New high end phones like iPhones now use eSIMs which are virtual software-based SIMs embedded into the device that do not use actual SIM cards. You download the information from the carrier to activate service rather than stick in a new SIM card. 7-11 definitely doesn't sell eSIMs.

@Michel ************

they don't buy any rooms, you must not know how OTAs work. They make a commission off every booking they send a hotel.

Like every country, Thailand has different visa requirements depending on what passport you are using and how long you are staying. No one can tell you since you didn't mention your nationality. Please add that info.

@Dianne ****

Good point. I assumed that they lived in Mexico but this is a good point to bring up in case they don't officially have Mexican residency.

@Matt ***********

Dianne gave a very thorough answer. Your best bet is to wait till you are 50 to do the exact same visa as your dad. During however many months you have until then, it is a simple matter of using existing options for American tourists (your residency in Mexico has no bearing as Thailand only cares about your passport country). USA passport holders can enter via visa exempt entry where you just show up without any visa and show your passport (30 days, extendable for 30 more days each time you enter), or with either a single entry or multiple entry tourist visa that you can very easily apply for from a Thai consulate like any tourist could. Single entry tourist visas allow one-time entry for 60 days, extendable one-time for 30 more days, giving you 90 days. You then go to a neighbouring country like Malaysia and come back in either via visa exempt (30+30 days) or on another tourist visa (60+30 days). Or, get a multiple-entry tourist visa, which gives you unlimited stays of 60 days each time, within the 6 month validity period of the visa, so you would need to leave the country once every 60 days, for example, to take a day trip to Singapore or Laos or anywhere you choose. By the time you do some combination of those options, you've made it to age 50 and can apply for what is commonly called a retirement visa. Keep in mind that entering by visa exempt entry (without having pre-applied for a single entry or multiple entry tourist visa) is limited to 2 land entries per year, and is technically unlimited for air entries, but Immigration may question too many repeated visa exempt entries and ask you to apply for an actual tourist visa. Doing it a couple of times is not going to be any issue.