Can I apply for a new Non-O visa using the 65k income route after letting my current O visa expire?

I think it's highly unlikely that you would be able to get the new year extension.

The reason for that is; even though you meet the requirements for the new extension you would be applying for by using monthly income by transfer (which you said you have done every month), because you didn't leave the 800K in the account for 3 months AFTER you had that extension granted last year it means you failed to do is meet the terms of the banked money method. 😕

They would catch that when you give them the year transaction detail report for this next extension.

I agree, getting off this extension and starting over is indeed your best course of action (y)

Unfortunately I don't believe you're able to use the income by monthly transfer to get either the initial 90 day Non-O visa or the first year extension.

Given that you would prefer a date for your extension more to your liking I'd say leave the country, let his extension run out, get a new 90 day Non-O visa from the thai consulate in your country before you come here and then apply for the year extension from that

OR

leave the country, let his extension run out, come back in 60 day 'free stamp' (visa exempt) and apply for the in country Non-O visa at your immigration office.

Either way, starting over is the way to go. You should check with your immigration office about the proof of funds (monthly or banked) so you can make a plan to meet the requirements which ever way you go on it