From my hillwalking days (hips and knees complain now), I have a pair of Hagloffs trousers. They were what I regard now as stupidly expensive, but it was before the kids came along so we actually had some disposable income. They're twenty years old and still brilliant. Quite fitted but just the right stretch with re-inforcements and gussets in just the right spots. Water resistant, wind proof but with zips to open for ventilation. I wear them now when shooting guns and cameras, they work well for anything outdoors. Being able to put a knee down without getting soaked is a bonus.
These on Amazon look good for the price!