Hi there. We went in Sep - you can only go via Bangkok airways. We booked via travel agent in Bangkok - we checked bangkok airways web site and travel agent matched the price (plus visa fee) so probably might as well just book via bangkok airways web site.
Big choice of hotels to go to dependant on budgets - good reviews on this site. Its easy to arrange to see temples - you just need a pass for 3 days, get a taxi or tuk tuk (much better to see life going on) for the day and they will wait for you after visiting each temple. Have fun!
Thanks for your help Blueiron12