Try wearing a thin inner pair of socks as Stottie commented.
The extra layer will help prevent transfer of friction to skin in any foot movement. My thin inners are of a polyprop type material and I think this also helps 'wick' moisture away from the foot. (unless your crossing a creek!)
What I do for determining correct boot size, (length) is put the boot on loosely and then tap your foot forward until your toes are up against the front of the boot - you should then be able to get your finger comfortably down between the back of your heel and the back of the boot without any 'play'.
Slogger, re' leather boots requiring 'break in'. My last two pairs of boots have been Asolo 535's, full leather, and I can honestly say they have been very comfortable from the first step and needed no breaking in at all. Had a pair of Garmont boots though, and they were never as comfortable even after extensive use. Though they looked very similar to the Asolo.