Anonymous participant a type O visa extension based on Thai wife is much better than the DTV. It is cheaper by bt100,000 too. And, you can work inside Thailand, getting a work permit, with it. It sounds more like you don't think the marriage will last.
Download the DLT Smart Queue app, and register. This will also give you the link to watch the one hour video, with timely questions to make sure you are watching, giving you a qr code to show at DLT at the beginning of the application process. It saves a minimum of an hour. Having the queue number saves lots of time. In Bangkok the main DLT offices across from chatuchak market is dept #5. I made the mistake of thinking it was 1, being it's the main office...lolol. By doing these, and having all the documents, you can be in, and out of there in less than an hour, and a half. I'm not sure if they've started having everyone getting a new Thai license take the written test yet, or not.
He will need a sponsorship letter from you, and you should have the equivalent of bt1million to be on the safe side, as changes are made weekly as abuses are tallied. What was allowed last week isn't automatically what is allowed this week.
You can take the night train to Nong Khai, cross the border into Laos as soon as you get there, then immediately cross back into Thailand, getting another 180 day entry stamp, and catch the next train back to Bangkok the same day. They are only making people stay in Laos extra days if they are getting another tourist visa exempt entry.
Without a formal marriage certificate she will not be able to financially sponsor your application. If having a job in Thailand she'll be on a type B visa, which doesn't have a financial requirement on the employee, only on the business itself. For your DTV you will need the bt500,000 equivalent in your personal bank account for, at most locations now, for 3-6 months. If you were officially married then a spouse visa would be a possibility, with no financial requirement.
Anonymous participant do you have current personal income tax filings in the UK. Not business tax filings, but your personal income tax filings? That has a good possibility of being asked for.
From what you are saying, and your history, you are going to have a serious problem getting a letter from the company you work for stating that you can work remotely in Thailand, as on the DTV you can not legally physically work inside Thailand. You can only work for a business outside Thailand, and not doing work in Thailand.
Here is something to serious consider before you do anything. If you keep working for your current employer right now, before you start your own company, and he will write a simple letter allowing you to work remotely, then with the other documents to apply for the visa, you will get the visa very soon after you apply, as long as the equivalent of the bt500,000 has been in your personal bank account long enough (from 3-6 months at most locations now). After you get the DTV THEN quit, and set-up your own business to work contract work for your current employer. It doesn't change your five year visa. It won't affect it at all. Doing it this way makes it all much easier, as it sounds like your employer will work with you to make it happen. Just saying.
When you present appropriate identification they ask for in person then you immediately get your money as the account is closed at that point instead of frozen. They tell you they are closing the account, but in reality it is frozen first. Then when you either present ID they ask for to get your money, or it stays frozen until the account no longer has enough cash in it to pay the account fees.