Second device just for sleep tracking

[notorious.dee]

Years ago, I had a Fitbit and loved it. I really loved tracking myself, especially as someone who has really bad insomnia. I got a Google Pixel watch for Christmas, but it's way too big and bulky for me to wear to sleep. Could I buy one of the smaller, slim fit it devices and just use it for sleep? Would it connect to the app?

When I started searching this topic, I kept seeing the answer that if you connect to devices then the data would be like cobbled together. I don't plan on using the smaller device for anything other than sleep so would it really be a problem? 

Also, if it is possible, any suggestions on Fitbit devices that would work for what I'm looking for?

[JohnnyRow]

Unfortunately you cannot have 2 current Fitbit/Google devices connected to the same account.  It was possible with some of the older devices, but none that are currently sold. 
Here is a quote from the old Help section from many years ago which I have kept, which Help section has since been rewritten.

But it occurs to me that if you were just using it for sleep data, you wouldn't be wanting to combine data like most people want to.  Usually when people want to connect 2 watches, it like one to wear to work and one to go out at night, or such, and they want to combine calories and steps but I don't think that would be an issue for you.
   If that is the case, you might consider setting up 2 separate email accounts, i.e. a separate account for each device.  Though, to sync and see your data, on your phone you would have to log out of Fitbit acct and into the other each time unless you happen to have access to 2 phones that you could sync with.

As for which one, someone else might have more advice, but all models track sleep.  You would not need a "smart watch", just a tracker.  The Inspire 3 is down to $70 from $100 right now.  It lacks some features of the later ones but I think sleep tracking is the same for all.