For many years I was involved in cave exploration in Australia and overseas, We practiced what is termed SRT (single rope technique)
en.wikipedia.org/wiki/Single-rope_technique This was used to climb situations of 100m+ plus (in total darkeness, and in the middle of waterfalls) in very remote locations. It is very reliable and reasonably comfortable.A good climbing harness is almost impossible to fall out of even upside down - and are designed to be use for many hours on end.
Basically an ascender is at chest level attached to the sit harness, and a second is held in the hand with a long loop of rope for the feet. Movement up the rope is by repeated moving of the foot loop ascender up the rope, pushing up with both feet together, and sitting, supported by the chest ascender. Just add a abseiling device such as a figure 8 (you might have one used for a boom brake) for getting back down. (you can use the asenders in reverse but its slower). There is basically there is no way you can get stuck up a mast with this system, even single handed.
Two golden rules:
1. always two attachments points especially when changing from ascender to desender,
2, Reserve a 11m kermantle static rope that is not used for anything else.....do not use an unknown mooring rope that my have had a 30 tonne or more dynamic load on it....and is just waiting to let go!
If you want lots of info try his source:
he taught me many years ago before expeditions overseas.
Also if you look though the personal equipment area...on harnesses you can make you own perfectly safe harnesses etc. from seat belt webbing and simple knots.
‘
Vertical’ by Al Warild. Or it is also viewable for free at www.cavediggers.com/ He is Australia’s ‘best’ caver (if you judge best by he’s bottomed the worlds deepest cave and written a book and every year goes on at least 3-4 HIGHLY elaborate expeditions open to only the most ELITE of the world’s cavers. ‘Vertical’ is the BIBLE of SRT and it is not overly technical, easy to read, cheap, and he is an Aussie!!