Bed occupancy DIY sensor

I’ve seen people using 3 different techniques here and I’m trying to figure out what would be best for me.

  1. Strain gauge (start of this thread) on slats
  2. Load cell + sensors (essentially turning your bed into a large weight scale)
  3. Pressure mats

Numbers 2 and 3 seem like they won’t work particularly well with a heavy foam mattress. Is that true?