Much easier to apply for non-o in home country allowing you to open the bank account on arrival to Thailand, season 800k for 2 months and then apply for 1 year extension. Applying in Thailand is a catch 22: to apply for non-o you need 800 k balalnce but without non-o you cannot open a bank account. In home country application you use local currency bank account already in place.
Drawing money from ATM, even spending it on credit card is technically a Remittance to Thailand however can you possibly see how this moves from "technically" to "practically"? Yet another loophole. Please remember all above only applies if you spend physically more than 180 days in Thailand in any (calendar = tax) year at which point you become a resident for tax purposes. Personally i stick to max 179 days per year and do not wory about the rest, The world is a big place.
even if you regularise your tax status in Thailand there is a double taxation agreement between the UK and Thailand. You will never pay tax twice. Additionally the Thai taxable income is based on remittance and not worldwide earned income. But even when both principles are cleared there is currently a lot of loopholes and ambiguity and for the time being i would not worry too much. Search for some developments of last week on this matter (try TNT - Tim Newton).
Wise allows two fee free withdrawals per calendar month up to £200 in total - please check though current T&C. Anything in excess of above two criteria the charges apply. 220 baht is from the Thai Bank, unavoidable and hence always withdraw highest amount allowable (usually 20,000 but Krungsri Bank 30,000).,