It's not polite to remind your partner that you are a gross decaying piece of meat.- John Hodgman
I'm in the Apple HealthKit ecosystem, so if you're in the Android world, there is probably a different place for you. The starting point for this is an iPhone and an Apple Watch which is going to serve as the secure enclave and get your the basic move data - let's move on from there!
Smart Scale - you definitely need to be keeping logs of your weight and BMI over time, right? The Withings Scale (now Nokia) is the classic - it's been tweeting peoples weight for a long time and when you launch the Nokia Health Mate app, it syncs your weight and BMI data into HealthKit.
Sleep Tracking - You'll definitely just want to get the AutoSleep. In its simplest mode, if the last thing you do at night is look at your phone and the first thing you do in the morning is look at your phone, it's going to track your sleep duration. If you're up for wearing your Apple Watch while you sleep, then it will also track your sleep quality during that time.
Water Tracking - I feel like this should be easier than it is. My favorite on this is the Hidrate Spark smart water bottle it's reasonable priced, works, and the battery lasts months. The main complaint is that you have to open the app to sync. The other options I've tried is the Vessyl Prime and it never seemed to track accurately and the batter would only last 6-8 hours on a charge which made it hardly useful. I still hold out hope for the original Vessyl which can track, ya know, every thing.
Pulse Oximeter - I know it's silly, but I had this chronic cough and my SpO2 was always tracking super low at the doctor, so I thought, "I wonder if I could track this into HealthKit" and I could! The iHealth Pulse Oximeter works like a charm, syncs over Bluetooth LE and sticks data into HealthKit. It's easy to just run it at night as I'm on the scale.
Smart Temperature - the Nokia Thermo is a neato smart thermometer that scans across the forehead to track temperature and store it HealthKit.
Smart Toothbrush - On the ridiculous, but amazing, side is the Oral B Pro smart toothbrush which tracks all of my brushing to make sure I'm brushing the right amount every night. In theory, if your dentist is bought in, they can set focus areas and do other things inside your app. I don't have that, so basically, I'm just tracking that I am, in fact, brushing my teeth every night. I also asks you if you floss, mouthwash and tracks that, which could be a little more enlightening.
I have tried some other apps to manually track eating or caffeine intake, but manual never lasts too long before I give up and forgot to be tracking, ya know? It's gotta be automatic.