Ron is correct. You cannot apply for OA or OX visas in Thailand. HOWEVER, he should have added you can apply for an O visa in Thailand, from which you can get a 12 month extension, based on being over 50, provided you meet the financial requirements. You can apply for an SETV or METV in Hk, and convert it here. Sorry, don't ask my the fine points of how to, I use an agent.
Transferwise also issue a statement of your transfers, no-one yet knows what will or will not be accepted, but I am pretty sure between my bangkok bank statement and the transferwise statement I should have my bases covered.
yes. the op said his agent was charging too much, so I used what I pay for comparison purposes. I apologize if I tempted someone to save themselves a lot of time and bother and use an agent.