To make trimming easier, maybe you could use pruning shears or even tin snips? They have the mechanical advantage to make the cutting easier on your hands and wrists. Any idea how long it takes to soak through before your butt get wet? We have quality/lots of cattails where we live, but it never occurred to me to make a sitting mat. South American peoples have woven sleeping mats from palm fronds since the beginning of time. It's nice to cozy-up to nature for the obvious benefits, but it doesn't break the bank, either. By the way, instead of using jute cordage, part of the cattail leaves can be made into cordage for this. There are several YT videos showing how - lots easier than me trying to explain it. Cheers and hello from Alberta, Canada.
I’ve never had a cat tail mat soak through to be totally honest and I used to use them for sit mats in the forest all the time. Especially in Ontario winters! I didn’t have the time this round to do the cattail cordage but you’re absolutely right that you can make good string cordage out of it. ❤️