Necromancing this thread just to say thanks to everyone. This is one of the coolest things to me, and was a good showcase of the flexibility of both the tech and the community. It’s working fantastically as a “bed presence” sensor to help run my Goodnight routine (it was previously managed with just motion sensors, which are ineffective if I’m idly at the computer).
I bought the inexpensive Ideal Security mat from on Amazon listed earlier and on the Instructables link. Instead of stripping the wires, I bought a matching pigtail to connect the mat to the dry contacts, just for ease of use. I have 20 19 of them, so if you have (or buy) this model, I’ll give you one if you don’t mind covering the cost of envelope and stamp.
Also, as of this writing, that mat is super-cheap through Amazon Warehouse ($16 - $20 with an additional 20% off for a limited time), if you don’t mind cosmetic issues for a product we are covering up…