Fitness/Activity -All in one

[iMore Question]

Hello, I have decided to get back into shape like I was in high school. However, I am looking for a simple solution to keep track of everything- heart rate, calories burned etc- I'm starting P90x. I am invested in Apple products except the Apple Watch. I would prefer to have HealthKit keep track of everything instead of having multiple apps on my iPhone. Would prefer Fitbit, or something else, since Apple Watch might be too expensive for what basics I want. Any suggestions?