lol sounds familiar, resting your stomach/knees on the joists isn't very comfy
hate that filthy/dusty insulation they used in older houses
just make sure you're not sore from training the day before otherwise it'll be 10 times more of a mission lol
my foot's gone through plaster couple times got lucky both times it was on top of bulkheads...
we usually try to avoid working on old houses unless it's really worth doing ($$$) or it's for a relative/friend etc