

You can build a simple bed presence sensor using one of those pressure mats used to hook up to alarms in nursing homes and a water/leak detector (I use the aqara detector for this). You just have to strip off the end of the cable from the mat, find the wires that do the circuit inside of the mat (I just used the leak sensor to find them) and wire it up to the sensor. Boom, bed presence sensor! Of course, this doesn’t track your sleep directly.
I’m not an expert, but Graphene has before first unlock protections where your phone is encrypted until first unlock. So, if it’s for some reason re-enabled during boot (I’m not sure that’s the case), then your phone is already secure anyway.