I always fly Eva from LHR to BKK but their flights are nearly always full, even on Mondays and Tuesdays and that means the seating is somewhat cramped.
Eva Airs fares are usually the lowest for direct flights, also the airline is now known and used by many families, couples etc, so with these combinations plus the down sizing of the aircraft I expect BR067/068 to be usually fulllish.
The Premium Economy (Elite) fares are about £400 more than economy and in my opinion not worth it.
Therefore I am assessing alternatives.
Thai fly twice a day to BKK from LHR, is the mid day flight less