Thailand is interesting country, it boarders Malaysia, Cambodia, Laos and of course Myanmar (Burma) Islands like Ko Samui Island that is known for its palm-fringed beaches, coconut groves and dense, mountainous rain-forest, plus luxury resorts and posh spas. The landmark 12m-tall golden Big Buddha statue at Wat Phra Yai Temple is located on a tiny island connected to Ko Samui by a causeway. Quite easily accessed by catching train in Bangkok to Surat Thani, from there ferry service out to Ko Samui.
Bangkok is first class place to purchase cheap airline tickets. Massage services in Bangkok are pretty interesting, however countryside is well worth exploring. The markets in Bangkok and really interesting and yes you can get laid to.
I'd recommend you check airline ticket prices online in Thailand before throwing money down the drain in the UK of course at your own risk but I think should quite Ok.
Cheap flights to Bangkok from $384
Cheap Flights from London (LHR) to Bangkok (BKK) from AU$654 (Return)
Flights to Chiang Mai:
Thai Vietjet Air 1h 15m Nonstop from $74
Nok Air 1h 10m Nonstop from $89
Thai AirAsia 1h 15m Nonstop from $100
THAI 1h 20m Nonstop from $176
Over night by train:
1st Class A/C Sleeper 1,753 to 1,903 THB 1,453 to 1,653 THB
2nd Class A/C Sleeper 1,011 to 1,291 THB 761 to 1,041 THB
2nd Class A/C Seat 891 THB 641 THB
2nd Class Sleeper Fan 831 THB 581 THB
Or 11-hour bus journey from Bangkok to Chiang Mai will cost you around 600-900 THB