I live in the UK, and it is about your best bet if unvaccinated. New eased rules go into effect this Friday 2/11. Test before you come and PCR test on day 2 after you arrive. No quarantine for anyone unless positive.
No testing at all if vaxxed, just have to fill out a very simple form.
If you care about masks, there aren't really rules except for London public transport (buses and tube). If you have kids, they've handled it much better. Basically kids <12 haven't ever been messed with at all for vax or masks. It was a little bit more strict on masks in Scotland last time I was there in December but not much.
Entering the UK:
https://www.gov.uk/uk-border-controlThey also have a pretty information site for travel to all other countries, although it is specific to traveling from the UK so may be different for coming from the US since things are pretty political with the EU due to Brexit:
https://www.gov.uk/foreign-travel-adviceWe're going to Spain this weekend since they don't require any testing either. But they do require vax. We picked Spain over Italy, France, Germany, Switzerland, etc. since those countries have stricter policies. I think the Scandinavian countries have just eased a bunch so may want to check those out.
If you've never been to the UK, I recommend flying into LHR, check out London a couple days and then take the LNER up the east coast to York, (Berwick-upon-Tweed if you have time especially in summer), Edinburgh, and then Highlands (Inverness, Ft William, Glencoe, Skye, Loch Lomond... lots of good options, can't go wrong especially once the weather gets nice around May into the summer).