New boots shouldn't be hurting your feet. They should be snug, not tight, with a little movement in the heel that'll go away as the boot breaks in. They should not be rubbing in any place. I'd send them back if I were you. Only wear the socks that you'll be wearing while in the field. If you'll be wearing thick socks with the boots then wear them. But don't break them in with thin socks and switch to thick or vise versa. You might create hotspots or make a good fitting boot not fit.