What is the best and easiest visa option for retiring in Thailand as a UK resident married to a Thai citizen?

Non Imm O based on marriage 👍

O-visa marriage in UK a lot of paperwork can go into that later,so in Thailand,first thing,400,000 buats in thai bank account as soon as possible, (90days)first, then get bank account within the first month in Thailand ,apply for an extension (yearly) at the endof the second month,which gives you a month to get sorted out with the extension, you do the 90days reporting to immigration office each 90days till the third one when you ask for the paperwork for renewing of the extension which gives you two months to get ready for it at eleven months of the extension ,ps marriage visa is 400,000 buats in the bank ,retirement visa( 800,000 buat in the bank three months after)can go down to 400,000 buats, but as to be back to 800,000 buat three months before renewal, insurance (not needed with marriage visa)

Easiest is a regular 90 days Non O based on retirement before you go and do yearly extensions of stay in Thailand if you fulfill the requirements.