I got frustrated with off the self bed occupancy sensors that would trigger false positives when I laid out cloths on my bed, or false negatives when I rolled over in the night.
I made my own solution using cheap load cells that essentially turns my bed into a giant scale. The goal was accurate boolean presence but the accuracy ended up around +/- 1kg.
This was fairly inexpensive to build, around $100 in development and $100 for the final product. This could be done for around half the cost with an ESP8266 or RFM69, but I like the reliability and low latency of Ethernet.