Do you have a source? Like, I'd pay money for good sleep tracking, (especially if it's fitbit-level money... I would pay more) but everything I've seen thinks that if I'm in bed and quietly, say, reading a book, I'm asleep until I move.
If you buy directly from Fitbit's website, the satisfaction guarantee is 45 days so you have plenty of time to try it out and see how well it works for you.
It also easily tells between activities in bed (even motionless ones like reading or watching) vs sleeping (and all the assorted cycles). It also measures heart rate, breathing (and how many times you stop), and even snoring.