Switching Non Immigrant O-A to Non Immigrant O

[skorts]

After 10 annual extensions I am going to leave the country without a re-entry permit to kill off my Non Immigrant O-A (Retirement).  
 

I posted before and said I would go the U.K. and apply for a Non-Immigrant O visa giving me 90 days on entry to Thailand and then apply for my annual extension based on retirement. I got some very helpful replies thank you. 
 

Due to a change in personal circumstances I cannot now return to the U.K. this year so plan to fly from Bangkok Suvarnabhumi airport to Hanoi and return 3 days later Visa exempt. I will (currently) get 60 days on entry to Thailand and will apply for a Non Immigrant O and then annual extension based on retirement. I don’t want to apply for a Non-Immigrant O in Vietnam as my dates of travel are fixed and it will likely take more than the 2 working days I am there to get my application processed. 
 

My ฿800,000 is already seasoned in a Thai bank account. 
 

I will complete the TDAC before arrival with details of my condominium I own as my address in Thailand. 
 

Do I need to have a confirmed departure date from Thailand and a flight out? If so I will use an onward travel ticket https://bestonwardticket.com

 

Anything else I need?
 

With 10 annual extensions and not having left Thailand for over 6 years will the Immigration Officer think it strange I did not get a re-entry permit or am I overthinking things? 
 

If questioned can I just explain I am switching to a Non-Immigrant O visa in country?
 

Thanks for any help and guidance. 

[DrJack54]

15 minutes ago, skorts said:

Do I need to have a confirmed departure date from Thailand and a flight out? If so I will use an onward travel ticket https://bestonwardticket.com

Flying visa exempt the airline at departure may/will require an onward flight within the 60.

 

As for other questions re immigration at arrival back in Thailand your concern is understandable. 

If you say that you are going to obtain a Non O at immigration, I can imagine them saying "why not get visa in Hanoi. 

Push comes to shove then explain the reason as you outlined in the OP

 

Apart from that which immigration office do you deal with. 

Requirement funds from abroad for Non O application should not be required as the funds have been in Thailand for some time.