@CharlotteB18
Yes, it's pretty stressful trying to plan travel these days, especially with a big family group.
I suppose you could send one parent ahead as the scouting party and make sure that Baldrick's cunning plan works. :-)
The rules seem clear, so the restriction is not on UK citizens, but on anyone arriving from the UK (or other Red Zone country). So you take a short vacation in a Green Zone country and you should be able to enter Bulgaria OK.
From a Green Zone country, I don't think you need a PCR test. You can elect for home isolation for 10 days... but go to the hospital on day 1, and get a rapid antigen test. A negative result ends the isolation. This test is cheap here (20 euros ish) so six of those is a lot less than 6 x PCR tests in Germany!
The Green Zone countries are:
Austria, Germany, Estonia, Iceland, Lithuania, Luxembourg, Malta, Poland, Slovakia,
Hungary, Finland, Croatia, Greece, Denmark, Italy, Slovenia, France, Norway, Republic of San
Marino, Principality of Andorra, Principality of Monaco, Vatican City State.
Plus, the special cases (reciprocal entry):
Romania, Czech Republic
I'd guess there are cheap Ryanair/Easyjet flights to several of these (France, Germany, Italy, Hungary, Austria, Romania, Poland, Czech Republic at least). So I think you have quite a few options.
As you so rightly say, you also have to figure out which of these allows entry from the UK, without the covid passport. That will narrow the list, but should still be a few.
Maybe go to the city you've never been before? Prague is great, as is Budapest.
The special cases are interesting, so they are not technically green, orange or red. So they (CZ and RO) might be good just because there is less chance of Bulgaria changing them to the Red Zone while you're there!
I'd guess Romania would be a cheap place to have a couple of weeks vacation. But.... goes online... unfortunately, Romania has also put UK on their Red list. (Their Red means you CAN enter from UK, but you must do 14 days in quarantine.)
OK... no! CZ is out too.
Poland is OK for UK citizens... but without a Covid Passport you will have to quarantine for 10 days (early release at 7 days possible with negative PCR test or rapid antigen test).
France has put UK on their Amber list, so I think this is out if you haven't been vaccinated.
Italy? Need a PCR before arrival... and 5 days in isolation and can then be released if negative PCR test.
Wow... this is harder than it looks... :-)
Yay! Hungary is OK if you get PCR test in UK before flying to Hungary.