What sleep metrics are most important for her to track, and how important is the accuracy of those metrics? And more importantly, what does she hope the data will improve? Seems like there's a wide range of devices built for specific needs. For example, a sleep tracker pulse oximeter won't be too useful for tracking general sleep movement but pretty useful for detecting sleep apnea I'd think.
I have the Sense Sleep System. I loved it, but then the company went out of business and the device doesn't work now that it has no servers to connect to.