providing all that is expected sometimes implies that you are prepared and have everything that's required. A long term lease agreement with the residency certificate is further ammo in your arsenal. Assume you also dressed appropriately. Respect is a big thing here and banks consider themselves professionals.
I'm 10yrs older than you. In good shape and good health. Medicate for high blood pressure. Had and cured Hep C. Never been hospitalized other than for shoulders replacement (overnight). I'm happy to self insure. I'm from USA, so healthcare here is about 30% of USA and of equal or even better quality.
The existing condition exclusion is used to disallow treatment for related illnesses even when medication or cure has controlled the underlying conditions. Example if medication controlled high blood pressure exists, any cardiac event, stroke or kidney failure could be disallowed. For me, I won't pay a premium with the hope they will pay when it's needed. All the major insurers are subsidiaries of USA insurance corporations. Greedy bastards who are only interested in profits. Sorry, but I'm pretty jaded when it comes to insurance companies....
nothing required from UK. you will need copies of your passport, a residence certificate from immigration and a Thai phone number in your name to open a bank account.