I think Portugal already falls of the list because you have active income, so not low tax. Switzerland can be somehow low tax if you relocate to certain cantons, Bulgaria is 7.5% tax so also not bad, i don't know about life in these countries except for Malta..
Malta might be worth looking into, 5% effective tax, private schools for kids (in English), cost of living is low, low crime rate, great climate, and very polite and friendly locals in general. Property can vary in terms of cost if you are looking for a luxury villa or apartment it starts from 2500eur a month. Downsides︀ are it is very bureaucratic like pretty much all countries, infrastructure is horrible, there is︁ not public transport except for busses which are never on time and take very long︂ to get you from one place to another, so you definitely need a car, also︃ it's full of tourists it's pretty quiet now because of COVID but without COVID it's︄ full of people everywhere, even without the tourists it's full of people actually, so if︅ you are looking to find some quite and peace I am not sure you can︆ find it on Malta.