On break-in of new (leather) boots --

Something I got from the Wardrobe Department of production companies I'd worked with ages ago is that alcohol (I've used isopropyl straight from the jug) will quickly wet into tough boot leather and cause the microscopic fibers to loosen and slip, then quickly evaporates and leaves the leather alone so that it won't mildew or rot.
Wear those brand new boots soaking wet with alcohol. They'll shift to fit you and the way you move right away. Follow-up with proper conditioning oil and they stay supple and strong, lasting as long or longer than they'd have otherwise.

Another side-effect of this kind of break-in process is that if you'd had any hint of concern about foot fungus or stink, it's guaranteed to be history after an hour or two of doing your chores in alcohol-soaked boots!

Cheers
Tinker