Looking for advice on current rules.

A family member wants to visit in December for just over a week - I know a bit about the Thai pass and the 1 day hotel stay and test but I am just wondering what exactly are the insurance requirements and does a visa need to be applied for beforehand? Does the Thaipass act as a kind of visa or do you apply for the visa first then the Thaipass? The family member is vaccinated and coming from the UK.

Any advice offered would be really appreciated and I know they will likely change again before then but the family member is question is wanting to book soon I think so just trying to understand all the information to pass it on. Thanks.