An Oura ring. Some quantitative insight around sleep, heart rate, heart rate variation, temperature, etc. SUPER interesting to see how things change when sick, drink alcohol, etc. Also- I confess to not minding the tone/language the product uses for coaching purposes. It is not an asshole.
Relatedly, tracking food/calories/water consumption in the (free- no need to pay them) Noom app has been useful quantitative insight as well. Rare that the free version of a paid thing has any utility whatsoever.