Igna,
Simplistically BKK is normally very heavily loaded but there are odd periods when the flights will be quite open over 2 or 3 consecutive days but its difficult to know when these days are.
At the moment the flights look fine but its early days .. also we stop our service to MEL at the end of March ( we've surrendered YET another route to Qantas supposedly in the name of the JSA ) which could affect the loads to BKK ( having to connect there onto QF ).