Sometimes the seat map is available to frequent flyer members. Your other options are : Go to their website and book a one way ticket. Many airlines show the seating map before the payment option. Option #2 call the airline..... Good luck!
The very first thing you should do is go to the airlines web site and check the seat availability on all of your flights. That will show you how empty or full your flights are and you can decide what to do from there.
I flew to the US three weeks ago. 1st leg 787 20 passengers and the 2nd one 787 70-80 passengers.
Before you pay to upgrade check out the seat availability on the whole plane including premium economy.
If you live in Houston I would book your flight on All Nippon ( ANA ). Wonderful airline. They have a non stop from Houston to Tokyo and then Tokyo to BKK.
I have a question for you. I arrived on a Non-OA from the US. Extended it at Trat immigration for another year in December, exp. Dec 1, 2021. Is this visa still an OA or has it now transitioned to a Non O?
The reason I am curious is that Trat Immigration told my Thai wife and I that we couldn't change from an OA to an O in Thailand.