I used Staysure in the UK they included a certificate of covid cover at no extra cost and I was successful in my application with Thai Pass using it.

There are no age limits on Staysure's single trip travel insurance policies. Staysure Annual travel insurance Annual multi-trip travel insurance covers you for multiple trips in a policy year and you can get cover for a maximum of 183 days abroad, although each trip cannot exceed 50 days (reducing to 35 days if you are 71 or over).