Funnily enough I saw an ad for water detecting bed protectors for incontinent people at the hospital just yesterday. They seem to run a material like aluminium foil under the sheet in a pattern. Maybe worth looing into as these seem to fit the bill for what you need.
The ones I saw fit to a system to alert a call centre via the phone if the person wets the bed. I didn't see the price though as no need for one (not yet anyway!).
Yes, it is possible to contribute your own tutorial by creating a project on openhardware.io (it shares the same database as mysensors.org) and submit it for review. After publishing, I can "move" it to the mysensors.org site and you can continue editing it.
For long time contributors we can offer full editor rights which means you can update any article on the site. It's a bit scary to hand out this right to anyone so you'd have to prove yourself first
If something is wrong in the current articles, you can of cause pm us the error to be corrected.