A bit off topic but you're a rescue guy so you may be interested to know that we use a full-body harness for going up the mast and find it to be far more comfortable, useful, and safe than standard bosuns chair or recreation climbing harness.
I've never used a full-body harness, but I used climbing harnesses (*) for years when doing bow on race-boats, and find them far more secure (and comfortable) than a chair. I have one now, with a 4:1 tackle, for pulling myself up the mast when alone if needed. You literally can't fall out of one, even upside-down (I was at the masthead during a spinnaker broach on a 70-footer once, back in the day. Kinda exciting for a minute. I've always wondered whether I would have come out of a standard chair... ugh.)
(*) in climbing vernacular, what I have is actually a "hanging" harness rather than a climbing harness. The difference is that a climbing harness is supposed to be protection in a fall, they tend to be light and minimalist and really aren't that comfortable to sit in for any length of time. A "hanging" harness has wider waist-strap, wider leg-straps, and generally a few more utility loops you can hang things from (e.g, a tool bag). My harness of choice these days is a Petzl Calidris, but there are other good ones (Black Diamond "Big Gun", etc). They also make "canyon" harnesses which are pretty much the same design, plus a "seat" section.
I really wanted to like the purpose-made Spinlock harness, but the waist strap and leg straps are stiff and not padded, so... might be very secure, but not very comfortable. Plus the one-size-fits-all isn't optimal, as it's super-important a harness like this fits the user correctly...
$.02
Bruce