Whole body/Bed occupancy sensor with arduino capacitive sensing

For an alarm project, I am trying to create a sensor or a sensing system to decide whether I am in bed or not. I tried various methods and the most stabile results I get was due to use of capacitive sensing library on arduino,
The problem is that due to some error in the system capacitance between your body to the ground changes a lot in a day and my treshold value changes.
Is there any way to sense human presence in bed with somewhat good accuracy.
some methods I thought of are weight sensing / hall effect sensors and magnets / sharp distance sensor or hc-sr04.
none of them worked as I hoped.

thank you.

ps: I can share the data I get from the sensor and some different code tricks to make it work as I wanted.

Not in bed but in the room: CO2 sensor (from your breath).

Depending on whether you use blankets or not: IR camera (sees body heat).

Weight should be a good one: a simple FSR (force sensitive resistor) under each of the feet of your bed. It won't give your current weight but will be able to tell whether the bed is occupied or not.

Temperature sensor, thermistor one or more alongside. May be MLX90614 , non contact

Well for a out of box thought,
position a PIR sensor as close as possible to the bed,
use a servo to move a card over the sensing window to block it.

Have the servo block/unblock the sensor and play with sensitivity till it does not trigger on a empty bed.

Decide how often you want to sample..

Granted if your near weightless so you don’t register on a load sensor, and your wafer thin so you can’t be measured with a TOF sensor, and you don’t create a capacitance field then you likely won’t generate much body heat either, but maybe just maybe..