jay fai cannot be booked atm because the venue doesnt allow reservations and only has seats for walk-in ...not sure where youve heard its already booked. as of recent theres a service run by some college students called hewtamsang (look them up on IG). people will literally wake up at whatever time it is, get a ticket, wait in line for you, and update you on progress, eta, etc so you never have to leave the comfort of your home until its time to eat. Cost is about 1000bhat per table reservation (seats upto 6?) i believe but is variable depending on what time you want to eat (peak dining times = cost more). if you have money and dont care id suggest this method, the alternative is to wake up god awful early and get a ticket and come abck (hoping you dont miss your number being called, otherwise you go straight to the back of the line which means you probably wont eat there that day)
otherwise I suggest Khao in Ekkamai if you want upscale thai food. they also have 1 michelin star and price is comparable. venue is nice and quite easy to get a table