@Stephen ********
“My question is, while I’m there, will I be able to change my tourist visa to a 90 day visa to allow me to apply for a bank account”
This needs an explanation, because you like to do step two before you haven’t finished step one
You cannot apply for the “change of visa type” to a 90-days Non-Imm-O visa, without already having a Thai bank account.
And you cannot open a Thai bank account on a tourist visa or on a visa-exempt entry.
In order to get a bank account opened, you need to arrive on a 90-days Non-Imm-O Retirement Visa which you got issued in your home country.
On this visa you get stamped in for 90 days, and you are able to get a Thai bank account opened. You are free to use an agent service to smoothen and ease the process, it should cost around 5000 THB.
You needn’t apply for the 1-year extension, you can fly back before the 90-days stay permit expires. And return by next year on the same visa, again