One of the reasons why we always prefer to transit though BKK when flying somewhere in Asia: the free one hour massages for first class TG thai passengers.
As F TG passenger: you area allowed to get 1 hour either full body aromatherapy massages, or neck and shoulder 30 min + 30 min of legs massages for free, at their dedicated royal thai spa located right in front of the first class lounge.
as a business class passenger, you are allowed 1x 30 min massages, either legs, or shoulder.
It is ONLY for thai airways passengers. So if you are flying first with Lufthansa, or business class with singapore airlines or any other airlines, you do NOT have access to the thai spa in bkk airport. If flying with other airlines, you do have access to the lounge, but not the spa.
It always surprised me how many people did not know that rule, and every few minutes, the staff had to turn people away as they are not flying thai.
That is why we always try to book with thai airways when we fly through BKK.
If you have some time to go into the Bangkok town, our usual favorite and cheap spa is: health land spa
450thb for 2 hour of thai massage ! or 4000 thb ($122usd) for 2 hour of 4 (yes four !) hand synchronized massage. If you have not experienced 4 hand massage, you need to try it in Thailand (cheaper, better).
Remember to tip accordingly to better represent your country: they are not very well paid relatively (the only reason why those ladies ask you where you are from, before starting the massage, is to see how generous you may be !! They do not speak English very well, and they really prefer not to talk to you !!). The thai massage therapist are the best in the world: their hands are so small, but yet so powerful.
The weird thing with health land spa is if you call them directly to book, they are always fully booked. BUT if you ask the hotel concierge to call for you, it is almost always available.