As mentioned you need to apply for a non o over 50 retirement visa in your own country today!!!! If you want to have a chance of getting it approved before you leave for thailand as it can take from 5 to 15 days depending on the embassy. The rules have tightened a lot in thailand when it comes to opening a bank account which you need for your extension of stay when in thailand. You can open an account with your non O from your country so suggest you sort asap
Suggest if you need to be there for 4 months is apply for a non o over 50 retirement visa which is valid for 90 days then before it expires leave to a local country and then enter again on visa exempt for another 60 days. Having no 30 day extensions gives you a better chance of reentering without local immigration hassle
The only easy accessible 90 day visa is the non O over 50 retirement visa which needs you to be over 50 and have 800kbaht or equivalent in your own bank account, that of course would be for both you and your mum, other visa that give you 90 days or more take a little longer like the DTV or LTR visa. Other tourist visas onky give you 60 days per entry so are no different to visa exempt
If your flight company say yes then you should be good to go. They check typically because they are responsible for getting you home if you dont get through thai immigration. Hope you enjoy your trip 😊
Since you will enter on a 60 day visa exempt but have return tickets that are at 75 days you will need to check with your airline if that is OK, normally they would expect you to have a return ticket within the visa exempt period i.e. 60days. If they say you need an onward travel ticket then you will need to look at options to purchase a cheap throw away ticket to a near bye country within the 60 days
also remember the first year of your O-A visa is multi entry, but your second year is only single entry so you will need to purchase a multi entry pass or a single entry each time you leave thailand or you will loose your extension
I have read your post on many sites asking the same. If you meet the requirements of the visa application its almost guaranteed you'll be approved so stop messing about with tickets to cheat the system just buy the flights ✈️ you want ro use, upload the details and then fo.enjoy thailand. You are thinking too hard about this. I have always bought my tickets and always been approved for the visa. Some embassies will let you put flight details in others want the actually confirmation from your flight company.
You will need to be able to show you qualify through either a soft power course/agreement with an approved supplier i.e. approved muay thai school, dental treatment plan from an approved dentist or that you can work remotely showing documents to prove it. Once you have this the application is straight forward but as others have said you can only apply for a DTV outside of thailand