What sensor to choose to track human presence indoors?
Especially for a home hobby project I'd probably start with PIR (Passive InfraRed) sensors.  They are cheap and very effective at detecting something warm like a human body moving around.

However, PIR sensors will not detect static warm objects like someone sleeping or sitting still on the couch.  With enough PIR sensors around the place, you can probably infer where people are motionless by where you know there was movement and in what direction.  PIR sensors don't inherently give you direction, but enough of them activated in sequence does.  For example three sensors triggered in sequence in a hallway is a strong clue someone is walking down the hall in that direction.  If you saw motion of someone entering a room and then motion in the room, but nothing at the doorway, then you can make a good guess the person that entered is still inside but motionless.

This system isn't foolproof, but PIR sensors are cheap and remarkably sensitive, so with enough of them I think you can get to quite a useable level.

One thing to keep in mind is that other warm moving things will trigger PIR sensors too, like pets moving about.  If you have a dog, then aiming the sensors so they only see motion a few feet off the floor helps.  Cats jump around a lot, but are smaller, so maybe there is a way to not trigger on cats.  This system will be a lot easier if you know the only warm moving things are humans though.