Rae, my jeans collection is fairly extensive. A couple pairs of skinny jeans I'm hanging onto for I have no idea why; couple pairs of straightleg, and easily a couple dozen boot cuts. My favourites of which are cuddly soft and as faded as the dickens. They are also frayed at the hems and seams, no holes, though. At least not yet. Like you, I haunt the flea markets and other thrift stores so I didn't have to do the hard work myself to get them like this. Only a very few have a slim knee break, most are full enough just below the knee to handle a cuff top boot with out it showing through. As long as they are tight from the waist to the knee I'm happy.
To answer you question about whether the boots will be worn under or over, it's always under, with all my boots.
