A more sensible option would be for you to buy a condo in your name. You can have any legal framework to lease the land but if anything goes wrong with the relationship you can have serious problems.
Non O is your best option. No need for travel insurance through Thai approved Companies. Apply for Non O 90 days whilst in the UK. Travel insurance can be very expensive. Really depends on your age and health. I eventually took out annual travel insurance but cover is restricted to 55 days. Other UK banks can provide travel insurance. For Thailand Insurance providing heath cover I tried AXA Sawasdee. Alternatively try an IFA based in Thailand
The ask:thailand community, consisting of multiple Q/A groups with over 100,000 members, powers this platform. It is not an official government resource. Our members actively contribute to this resource, and while we strive for accuracy, we cannot guarantee its complete reliability. Assistance to travelers is provided as a community service.