I've used forwarding services from the US to the UK without any problems. US-UK is complicated with taxes and estimating postage. EU ones will be a lot less hassle but they all seem to choose the most expensive couriers like DHL and Fedex for some reason.
https://mygermany.com/
https://www.trustpilot.com/review/mygermany.com
seems to have good reviews and gives you a German address. They ship to Greece too.
Sometimes the complicated and not-so-well-regulated tax regulations in Greece forces companies not to bother. At least that's what one representatives of Overclockers UK shop told me. Those guys ship to Cyprus but not in Greece so I was like "WTH?!".
Thanks for your suggestions, I'll look into them.
UPDATE: I tried their calculator with dummy data and the price seems fair. A 27" monitor which is sold for 700€ and which I calculated to be about 5kg, also insured for 500€, would cost me 30€ with DHL (not delivered to my door I think but that's ok). I'll wait for the crypto prices to hit new highes and by then, I'll probably find a monitor with 2k, 144hz, Gsync and HDR to buy!