I've used (a) the Beddit touch-sensitive mat, (b) the Fitbit watch, and (c) the Oura ring. Beddit claimed I never slept more than 2 hours a night, which was something of an exaggeration. Fitbit was better, but I still caught it a couple of times claiming that I was asleep when I was actually lying awake reading for an hour. I've been using the Oura ring for maybe 6 months and I haven't caught it in any known mistakes so far; there was one weird thing where if you had multiple sleep periods separated by several hours, it'd show only one of them in the cloud view, but I've not hit that recently.

I would recommend the Oura ring with few reservations.

I have a Xiaomi fitness band 2. As far as I can tell, the sleep metrics it reports are pretty good. I wouldn't attempt to compare its accuracy to an Apple watch, but the Xiaomi's battery charge lasts about a week and it cost $30.

Withings (ex Nokia) is selling mats that you put under your sheets and where you lie on. I think Apple does, too, but only in America.

That's probably the best device for home-use. But sleep labs are using EEGs, cameras, microphones and puls oxymeters for a reason. Don't expect medical-grade results from a home-use device.

Less accurate are several kinds of fitness trackers/smart watches, very inaccurate are smartphone apps.

I don't know what specific devices they may have had in mind, but one accessible way to track sleep is with a smartwatch.

I use a Huawei Watch 2, and it tracks pretty accurately from what I've seen. Other Wear OS devices are probably similar.

I personally find the Oura ring to be great at tracking sleep stages and various biometrics during sleep like HRV and body temp change.

I have a Luna smart mattress topper. I think they rebranded to Eight or something. Pretty good stuff.