To clarify, you're seeking a temporary residence permit for one year based on marriage, which requires a Non-Immigrant visa. You can apply for a 90-day Non O visa outside Thailand or switch from a tourist visa in-country if you have a bank account.
Over time, an increasing number of immigration offices have discontinued the practice of accepting monthly income or pension transfers from abroad as grounds for extensions based on marriage. While some offices may still accept this in practice, as evidenced by feedbacks, the prevailing rule is now otherwise, and the alternative has been formally removed from the regulations.
You’ll need to ensure that funds are seasoned for two months in a bank account prior to applying for the one-year extension of stay, which should be factored into planning.
Then you are not on a legitimate stay if you have used an agent to circumvent the formal requirements for an extension of stay. At some point, you may face consequences due to the current crackdown on banking services.
Then you’re not on a legitimate stay if you used an agent to bypass formal requirements for extension of stay. One day you might run into issues with the crackdown being done on bank services these days.