https://www.google.com/search?rlz=1C1GCEU_enUS821US821&ei=Xl3kW6zKBJGZ8AOqtbfwBA&q=home+assistant+bed+motion+sensor&oq=home+assistant+bed+motion+sensor&gs_l=psy-ab.3..33i22i29i30l9.12142.14833..14929...0.0..0.87.836.11....3..0....1..gws-wiz…0i71j33i22i10i29i30.6Q3xwhVq4cA
Found me this: Bed Occupancy Sensor