Human/inanimate isn't the issue here:
Shoes, like gloves or stereo speakers, function best as a matching pair. But most books, tins (US: cans) of food, etc. are useful individually, so I could reasonably buy a couple of books etc.
Pair refers to exactly two items (animate or inanimate) that belong together; couple of applies to a possibly disparate collection of maybe 2 - 4 animate or inanimate items.
I'd translate "boot" to "but", there's also the augmentative "bucior" which sounds kinda colloquial. I've worn military boots many times (my father used to be in the military so he could get them easily) and I never called them differently, they were "buty wojskowe" to me.