I track mine on my Apple Watch which records it in the Health App. It's basic graph and I can download it if I want, but I've found tracking day-over-day/week-over-week is a good enough signal. For example, I did dry January this year and practiced meditation every day since and I've seen a step-jump up corresponding to that.
Still have to keep another record of external factors to correlate with it, though. I've heard people finding success with a 3p monitor and the Elite HRV app as well [0].
I've never had the WHOOP, but I use Apple Watch combined with iPhone apps to track heart metrics. I recently discovered AutoSleep and HeartWatch, which both track HRV along with other metrics.
