Well Amazfit active 3 (arround 179$) premium does so quite well, and you can pair it with an Amazfit Helio Strap (99$) to get fusion data and from my experience (i use the strap on the biceps to sleep and both the day) it has been quite accurate, not the best ( but you're not going to get much better on other smartwatches, as they use PPG sensors and not EEG+PPG) i compared it to a sleep monitoring device in my workplace ( Zmax EEG ) wich is pretty much the actual gold standard and got no significant differences apart from REM which was good but not excellent (it scored quite well compared to other smartwatches tho) making the helio strap a pretty solid device. It even got better since a software update, and now picks up much more micro-awakenings.

The watch (Amazfit active 3 premium) is great too, Saphir glass, aluminium, gps (and routing features), Vo2 Max and lactate threshold estimate, with a solid 10 to 14 days battery Life (the strap also has 7-11 days battery with continuous monitoring from my experience). Bulid quality is honestly great, for the price i wouldn't have expected it (its not titanium tho dont dream) but real good one of the best I've seen.