This might help…. add climbing harness as safety backup.
“How to make a Belay Seat
Setting out on a big steep wall sans belay seat is not a good idea. I’ve met climbers who spent days sitting in just their harness and suffered long-term nerve damage in their legs because of it. The best way to get a belay seat is to make one. All you need is a piece of plywood, some cord, gaffer tape and a sit mat. The wood needs to be about a third wider than your hips and thick enough to inspire confidence when hanging above the abyss. Getting a piece of wood that’ll slide into the back of a haul bag will help give the bag some support when being carried.
Gaffer tape the sit mat on to the top of the board. Drill holes in all four corners. Then take around five metres of 8mm cord and feed it through the holes so you end up with a kind of swing effect, with the cord crisscrossing underneath the seat, with the knot tied with a double fisherman’s underneath. And now you’re ready for some 10-hour belay duty.”