Oliver,
I think that, as others have said, you're OK in Holland without mode S if you stay below 1200'. There's anectodal evidence on various fora that ATC may, on request, allow you above this altitude even if you only have mode c. Thge bigger problem with Holland is that it appears the Dutch require you to have a fixed ELT. A PLB is apparantly not an acceptable substitute.
In Germany if you stay below 5000' then you don't need mode s