App + Machine to "automatically" record when I go to bed.

My sleep schedule is very unstable and I want to invent a machine to record when I go to bed. I will use this to correct my pattern. I found a software but that was not for me because users should click and record by themselves to use the software. Then people will not have motivation to keep recording it. When I just lay down on my bed, I want the machine to automatically record that I started to sleep. I thought of installing a button below my pillow, or some other things but I am not an engineer graduate so I can't figure it out. I also thought of some machine that will detect my presence on bed. But I don't know how to do. A mobile app alone is not enough because I need to record it automatically. So I will need both app and machine. ANY IDEA is good. If you only have ideas but don't know how to make it, that's also OK and I will ask an engineer if it's possible to make it and if yes, I will pay accordingly.