The solution? We realized we had up to eight inches to play with between our wardrobe and the woodbox we're building for the stove. We measured our shoes; they would only need shelves six inches wide, and that would still leave room for the sides of a shelving unit and a firewall for the wood stove.
We built shelves the height of the IKEA wardrobe we'd already assembled, inserted six-inch-wide shelves, painted it all black to match the closet and, viola, all our shoes and boots have a home. Because the armoire is 24-inches deep, a pair of shoes can slide in each slot.