@Bernadette *******
Ok. But why the O-A? That's the one you use money in own bank wherever it is, mandatory insurance from a limited selection of Thai insurers that aren't the best, police clearance too. Then it's only valid for periods the insurance is for.
The Non-O there's no police clearance and no mandatory insurance ( you can choose what you want, when you want ) but you need to open a Thai bank account when you arrive and bank 800k Thai baht. Then extend for 12 months which costs 1900.