I've always used WorldNomads.com for my travel insurance, and their coverage appears to far more extensive than the packages as recommended on the ASQ.in.th or ThaiEmbassy.org sites (for similar costs).
As long as our policy explicitly covers +£100K of Covid19 treatment, are we allowed to use our own preferred travel insurance when entering Thailand?
TLDR : Answer Summary
Travelers can use their own travel insurance to enter Thailand as long as it explicitly covers Covid-19 treatment with a minimum of $100,000, and it adequately covers the duration of their stay. However, issues may arise if the non-Thai insurance does not cover hospitalization for asymptomatic Covid-19 cases, or if reimbursement processes are not direct to hospitals.