Photograph: Julia Forbes Like any Sleep Number smart bed, the ComfortNext Lux offers 100 firmness levels, and the one you select is your “Sleep Number,” or the firmness you prefer to sleep on. I usually skew toward firmer for lumbar support and weight distribution, which has previously been in the 40 to 50 range. Then, a new recommendation popped up in the app—my firmness level was in the mid-70s, but going softer could improve my sleep score, which Sleep Number calls its “SleepIQ score” and reports in its app. I decided to lower it to a much softer firmness level of 35. The SleepIQ score summarizes your nightly sleep metrics, including heart rate variability, breathing rate, and time spent in each sleep stage. This data is compiled into a score that summarizes your sleep quality. The app’s score always skewed lower than what my Apple Watch SE would track. However, with dogs jumping in and out of bed, the sensors track that motion and take it into account, too. Despite this, my Apple Watch showed …