Another option is O-A visa, your financial requirements are UK based, £20,000 in a UK account for 1 month but you will require a police check - a DBS is £18 and takes about a week; Medical certificate (see link for requirements
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-non-immigrant-visas); 100,000 USD insurance from specific providers. AXA is a cheap bare bones policy which will suffice for visa.
With this visa, you can potentially get 2 years from it. Your first year is multiple entry, when you arrive you are stamped in to the end of your insurance (so make sure it starts the day you arrive). If you exit and re-enter before the visa expiry date, with a new 12 months insurance, you will be granted another year stay. The 2nd year is not multi-entry but you can buy a single or multi re-entry permit in Thailand.
It does have its costs with the insurance but if you want to have the least contact with your local immigration, it's a good option. It's exactly why I have it, as my immigration office are difficult.