I'd say that is a tight connection given all of the variables (arriving gate location, immigration queue, wait for baggage). Bangkok Airways requires passengers to check-in 45 minutes prior to departure. Also you will have to be bussed to the plane.
FWIW there is no separate domestic terminal per se. (There is a domestic concourse.) You will exit Customs at level two. Look for an elevator, or escalators, and proceed up to level four, check-in row F, for Bangkok Airways.