I’m not an expert on European options, but in the US I’ve been really happy with Virtual Post Mail.
They are quite reasonable for modest volumes of mail (I think $15 per month is the current starting price). The UI is also much better than the other options I’ve checked out, being fully responsive so easy to use on mobile, too.
They only offer one address location, though (California, near LA). So if you need something else, have a look at Traveling Mailbox. They offer quite a few locations.