Long Stay Travel Insurance (EU)

I am working in Germany and Luxembourg for the next 18 months and am covered by social insurance in the countries where I work. However it does not cover travel outside any of the countries I work in, which as Luxembourg is quite small means that I am not covered virtually every weekend when I go out or shopping.

Can anyone advse in an affordable and reliable option?

I tried American Express but there gap year insurance (which could have covered me) becomes void on any trip back to the UK or the other option is constantly having to buy new EU annual policies due to the limits onstays abroad . I have also come across another company called Navigator (https://www.navigatortravel.co.uk), but have no idea how reputable they are.

Any advice would be welcome.

cheers,

rod