Moving and lifting straps (Shoulder Dolly, shown here, is one type; available at amazon.com) take the weight off your back by relying on leverage and large muscle groups. They also leave your hands free to maneuver awkward items. However, they can be tricky to use on stairs because the weight shifts completely to the downhill mover.
Look for lifting straps that can be adjusted for different-length objects as well as for different-size movers. The Forearm Forklift Lifting and Moving Straps shown here are great for moving on flat surfaces. These and others hump straps are available at home centers and online.