Use a climbing harness for going up the mast
As a rock climber, I have more faith in a proper climbing harness - it fits snuggly around each leg, and your waist - than in a bosun's chair. Because of how it fits, you can move around a lot without any fear of falling out/off of it. To help the wincher, you can actively "climb" the mast by pulling down on part of the halyard that is being winched to pull you up. You get up the mast a lot faster and your winch grinder's more likely to buy the beer afterwards! For safety, you can keep an extra halyard cleated off at the deck and winched tight. Then run a small rope from your harness to a prussic knot that you slide up this 2nd halyard as you move up. If the main halyard failed, the purssic would tighten around the 2nd one and arrest any fall.