Poland and Hungry are a bit close to the war and the next option is places like Norway and Sweden not really beach weather. Being honest only place which appeals is Dublin.
I would have suggested Switzerland as there are now no longer any domestic restrictions, but unvaccinated people can still only enter if they are Swiss/EU citizens or meet one a limited number of criteria.
The following map
from the Sherpa website indicates which countries are open to unvaccinated people from the UK. Those open without any testing/quarantine are dark green, those open with testing are light green and those not permitting entry are orange.
So as you say, most of the countries that are restriction-free do border Ukraine, Russia or Belarus (though if you are in the western part of Poland or Hungary for example, I wouldn't consider this risky at all).
Slovenia, Montenegro and Czechia don't border those countries and are restriction-free, at least in terms of arrivals - masks are still required on public transport in Montenegro and Slovenia.
Alternatively you have Iceland, Norway, Sweden, Denmark or Ireland, all of which have also scrapped domestic restrictions including masks.