I am in the process of doing this myself. if you already have health insurance, by one of the approved insurance companies, I would apply at an embassy out of the country. The problem coming in with a tourist visa and then converting it to an OA is the opening of the bank account. some people say you can go to the immigration office, get your certificate of residency and open a bank account with this. I ended up hiring an agent and having to use a specific bank that charged me for insurance that I felt was a poor value. The total amount spent was about 10,000 baht or $300. Shop around as the costs for hiring an agent vary widely, with the money transferred to my bank account I then went to the immigration office and had their volunteers help me fill in all the paperwork which was turned in last week and accepted by my local immigration office. It appears as though I'm at the stage in the process by which we are taking the steps bringing the proper papers again and following directions of the immigration officers, pretty straightforward, good luck.
Free, go to the immigration office in your area. there will be people called volunteers that will step you through every step of the form and what forms you need to have. in addition there will be an office there that can take pictures and make photocopies for you at very reasonable fees.
hire an agent, I'm assuming you're in Thailand? I would get into my Google maps application and call all the agents asking them how much it is to open an account and use one. The days of opening an account with the bank on a 60-day Visa from my perspective are done.
I did one in California about 6 months ago. they were really strict about identification, so I had to show them my driver's license. I believe it was actually an FBI search for criminal records. something tells me that you're supposed to be there in person before they'll run the background check which is why you have the shady sites. Good luck!
I've been on the road for the last 5 years and have always had a stable address for governments and banks. however, banks will not send credit cards nor governments passports to a pobox. most mail is opened scanned and sent to me via email/app at my request. The other documents / credit cards all need to go to a relative first and then be forwarded to me. In states such as South Dakota, a Mail forwarding address and one night in a hotel every 5 years allows you to vote, have a driver's license, and become a state resident with no state income taxes.