You may want to consider international health insurance through a Thai insurance company. The procedure is similar to an application for a western-based insurance company.
In general, it is sufficient to complete a health questionnaire, and in some cases, a preliminary investigation may be required.
Like in western countries, Thai insurance companies offer various insurance benefits, such as choice of hospital, private accommodations (single room), etc. The insurance costs are usually approximately 60% of the cost of a comparable insurance in western countries. Unfortunately, some insurance companies have a maximum age limit for their health insurance and do not accept those applications.
We are happy to advise you in this regard.