Device better for sleep tracking

[christyvido]

What should I look for? Heart rate monitor?
Any specific sensors I should look for?
Smartwatch or Fitness tracker?

My goal : Sleep tracking, Heart rate (all day), Respiration Rate (all day), (plus any health metrics I can get)

Your perspective and recommendation will be much appreciated.

[emili]

hey there. are you asking which model fitbit would be right for you? They are different in style, size and price. They all pretty much have the same metric information. I would peruse this link  to see what models are available with which features that you are interested in. 

[Rufous44]

@christyvido no Fitbit can be suitable for you as one of your requests is to have Respiratory rate all day and Fitbit provides such metric only during sleep.