As for trousers I like the old British army lightweights be as they were designed to be worn high and NOT on the hips.
this sounds like the 'chamois cream' cyclists rub in down there, originally used to break in real chamois pads in shorts. It's awfully expensive, so I just use cheap Aqueous cream B.P and it does the job...I use some cream I made from shea butter, olive oil, and some other stuff, (I'll find the recipe and maybe post it here.)
I rub into the affected area, also on my feet before a good walk. It stops chaffing and it's odourless, and it does not stain clothes either.