If i would be in ur place i would do my itinerary myself. you can find lots of write up about Thailand here.. just also search web for places to see. make ur itenary. then visa is on arrivl and also till april no charges. hotels or hostel you cna book online. airbnb was my mode of booking when i went also search trivago, agoda for better deals in hotels. Also packages with chukey and patrata wil be difficult to get. so plan urself so u can finish everythng in budget. check skyscanner for best flight deals.
Check the flights on skyscanner.
Check the hotels on trivago/mmt/booking/goibibo/agoda/yatra/expedia.
Check the sightseeing tours on isango/klook/viator or you can book them there too once u reach thailand.