Hello
Since I have just returned from this trip I thought I would post a reply based on my experiences.
First, regarding the transit facilities in Bangkok...apparently they are INSIDE the arrival area, not OUTSIDE, as I was told when I asked in Bangkok. So, I never did find them. The only facilities outside the arrival area (in the unsecured part of the terminal) are the CIP day rooms which have no facilities expect a bed. Not what I needed.
Second, I did stay at the Amari on my return flight. It is not simple to find from the domestic terminal. The Amari is located across from International Terminal 1. I was traveling on Thai airways and just walked up with no reservation, so I was able to get a room for US$130. The regular rate is US$260.
For $130 the room was okay. I only wanted to sleep and make my next flight out to the US at 6am. I suppose if I had been more alert I could have been more critical, as I noticed that the carpeting in the lobby on my floor was terribly dirty and stained. But, my room was fine.
It is only a short walk to Terminal 2 where my flight left. I left the hotel at 4am. That was too early by at least 30 minutes.
Happy to answer any e-mail inquires.