Does you pension meet the minimum requirement? If so, the paperwork should not be hard to get. I down load and print a letter for verification every year from a website.
A dog that small can be carried as luggage in a soft case that fits under the seat. Check with the airline for requirements and Thai customs. The paperwork was not hard just follow all the instructions. The coat should not be more than a few hundred dollars.
In 2013, I brought a britney dog to Thailand in a cage as checked luggage. The airline charged me $200, and the vet BS was less than $100. The airline checked everything but Thai customs didn’t check anything just asked me the value of the dog for taxation.