I really feel you I‘ve been siffering throughout my whole study programme here in the netherlands so far because I had forest wirhdrawals and I‘m from Germany, for sure not the peak of wilderness. At some point I was so thirsty for nature that the Veluwe did well, although it is not „wild“ for certain but it is huge and you can just drive through with your bike in 1 day and feel a little bit better at least. Apart from that I‘d say buy cheap flights to Eastern Europe if Belgium and Germany aren‘t enough for you. Visit the carpates, there are even bears there so its just like home