you'll have access to the *G lounge(s) through your onward boarding pass to BKK. I'd recommend you hit the non-Schengen OS lounge (right towards the central part of the terminal) before going through passport control and freshen up there. By the time you are ready, most inbound flights from US (arriving within 45min or so) will have unloaded their pax through passport control.
For a quick and easy ride use the "City Airport Train CAT" leaving :09 and :39 every hour; the regular commuter train S7 is somewhat cheaper with a few stops along the way.
DAvid