I use an agent to pay the money into my account ,this allows me to leave my money in a higher interest account in another country ,the interest on £18,000 (800,000 baht) more than pays for the agents fees to sort my visa yes an agent is much more expensive but you money in Thailand won't earn you any interest, Financially its cheaper to use an agent
A non O is better no need for police reports or Insurance, you get 90 days then you extend it to 12 months, then is 12 months every year you renew. You are allowed to open an account on a Non O visa
While you have a non o visa get a residence certificate from immigration and you can open a bank account I would stay away from Bangkok bank and use Kasikornbank, the reason people account are being frozen has got nothing to do with agents opening them its because the Bangkok bank allowed 40 million account to be opened for money laundering and got caught ,so now they need to find those accounts.
Once you have you bank account its easy the bank account is the bit agents can't do.
You will need 800,000 bht in the account an agent can do this for you obviously at a cost around 30-40 000 bht but your money will remain in your country earning interest.
I know 800,000 bht is about £17-20,000 in the UK this will earn enough interest to pay the agents fees and has some left over ,the renewal is much cheaper so the interest on the money more than pays every year.
that's exactly what I put below an hour ago but no need for an agent to open a bank account for you as is nearly impossible these days without the Non O visa