@Lee **********
, you need to get here, get a place and then open a bank account and get the 800K baht transferred in as quickly as possible so you don't run out of time on the free 30 day entry stamp you will come in on (although you can get a 30 day extension on that free entry one time for 1900baht to buy you a little more time).
I'd say once you're here, GO to the immigration office in the area where you live and get the hand out listing the requirements for the Non-O 90 day visa.
Then you will know what you need document wise, but you won't need anything from the UK other than your passport.