You can check out the likes of TransferWise now Wise and the one I not dared to try Revolout. All of them have different benefit. I use Wise as my travel card which they supply for free and load it with my currency for spend in other countries. The conversion is decent enough for me to not look at others as is. I am sure there is more actors out there and cheaper ones.
Yeah they also got higher speed for 300 THB. I noticed they got some good packages if you use Rabbit LINE Pay. Because I had some issue buying the my old package in the app.
Honestly last time I went to the ATK in BKK they hardly swab my nose. It is very unlikely it will be positive. Before you leave home do your own ATK and make appropriate plans based on that.
I would consider getting J&J if I was in your situation and discuss with the local Thai embassy how to proceed.
Insurance is available in many forms if you have a US one that can give you overseas cert for the amount stated for covid that can be used. Else just buy any recommended in this group.