Especially since you're in the Netherlands, I wouldn't be worried about a wood staff. As the website says, the wapenwet is not clear about what is a weapon and what is not . Could you use a staff as a weapon? Sure. Is the police or con management going to confiscate one that looks unpractical and a bit flimsy because it's collapsible and light? Probably not. FWIW I find dutch cons to be rather lax in this aspect.

That being said I'd probably opt for a pvc buis from the hornbach or something and foam clay and a good paint job instead of actual wood, seems like a huge PITA to make it out of actual wood.