I cut a pair of thin wool slacks into shorts and they are nice for all kinds of activities. Some trousers are made of really fine wool that isn't itchy so use those kind, I can usually get 'em at the thrift store for less than 10$ a pair usually... I usually get charcoal grey slacks for cycling, very versatile colourl. I also take out all the pockets and sew them shut. Wear them with a cycling shirt or any other non-cotton shirt. I've thought about sewing a chamois into them but haven't really had a need to do that. Easy to wear cycling shorts underneath too since the pockets are gone. If you pack long wool socks they are good in the cool weather too.

tl;dr google "DIY cycling knickers"