What's the best iOS app for detailed sleep analysis and daily readiness scores?

Oura is a health monitoring application that syncs with the Oura Ring wearable to provide in-depth sleep analysis and readiness assessments. The app tracks sleep stages—including deep, light, and REM sleep—and generates a sleep score based on duration, efficiency, and restfulness. Its readiness score, calculated from factors like heart rate variability and previous sleep data, offers a snapshot of the body's preparedness for the day. This functionality is particularly valuable for athletes adjusting training intensity or individuals managing health conditions, as user reviews indicate cancer patients rely on it for heart rate tracking during treatment. Specific features include continuous heart rate monitoring, activity logging with personalized goals, and temperature sensing that can signal early illness signs. The interface presents data clearly through daily summaries and long-term trends, encouraging lifestyle adjustments. However, the app requires the Oura Ring hardware, which involves an upfront cost and may not accommodate all finger sizes; some users report needing to switch fingers due to swelling. Reviews also note occasional durability issues like ring separation, though customer service is often praised for quick replacements. Despite these limitations, Oura's holistic approach to health tracking makes it a strong choice for those prioritizing sleep quality and recovery insights.