yes you can extend your TR visa for an additional 30 days. In Bangkok, they are currently not giving the extra 60 days for a covid extension, as you're eligible for the 30 days. who knows what will happen in a month or so time.
As for the converting to a work permit, i'm not sure, but i don't see why it couldn't be done.
Well you’d need to have your flight and asq booked for your return in august (and who knows what flight options will look like at that time, and if asq will still be required or how long it will be) in order to apply for your COE. So as others stated wait until closer to the time you want to come back. But I wouldn’t leave it too close to get your COE as some embassies take longer then others. In theory it takes as little as a few hours to get the COE up to a week or longer.
there are no specific restrictions for people from the uk. It’s the same requirements for everyone from any country in the world. Some can come visa exempt (same countries that could prior to covid) all others require to apply for a visa.
that’s a visa. Visa exempt means you don’t have to apply for a visa to come into Thailand. It was previously 30 days. But it was stopped last year due to the pandemic. They just recently started again. Then changed it to 45 days so travelers could still get 30 days out of quarantine.
Nobody knows for sure what the situation for immigration will be. Some people are staying you’ll be able to get the 60 day covid extension but that’s not confirmed as the official last date for those is Jan 29! But that may be extended. Keep your ears open as to what the govt announces next week.