One safety precaution you can take is pretty simple, and could save your life. Have a second halyard in place and tie a Prusik Knot to it and then to your bosun chair (better yet to a separate climbing harness). Google Prusik Knot and there are tons of videos on how to tie it. You only need a small diameter chord (relative to the halyard), 5 or 6mm is good. It's so simple you can't tie it wrong, it slides easily on the halyard as long as there is no weight on it, but as soon as you put weight on it it locks up.
Some people use an "ascender" which is a device that has teeth that grab the halyard. The downside is this can damage the halyard over time. It's also about $100, where the Prusik is nearly free.
When going up the mast always assume: 1. the halyard will break; or 2. the person belaying you up will make a mistake. With a second halyard and a Prusik you'll be safe.