I'm a bit OCD about waist and hips measurement, and tracking my waist height ratio. So I got excited when seeing this thread title.
The hips of course - is your belly. And that, in my experience, is the measurement that fluctuates the most with daily food (yoga, posture, fatigue etc?) and so on. I think that is why it's the waist measurement that is used for the w/h ratio, as it is way more consistent. (That is certainly my experience.)
As for where your waist is. I poured over descriptions of where to measure for this, with centimetres over under your belly button and so on. I do believe those descriptions are meant for the males amongst us

. Because once you get a waist again (I did not have a see-able waist for decades), as a woman, it is incredibly obvious where it is. Or, I remember back in my youth for fitting Levis, seeing it described as the smallest measurement, which makes sense for clothes fitting. (And where your various organs are?) The hips/belly measurement is the largest part - again - very sensible when thinking about and measuring bodies for clothes. (And where the bulk of your digestive system is? Correct me if I have my body stuff wrong...)
It worked perfectly for ordering clothes online during the lockdowns, for sure.
When tracking my waist and hips/belly, I only measure first thing in the morning, before coffee and certainly before food, at the same time as my Fasting Blood Glucose. If I am keeping an eye on my blood pressure, this is when I take a baseline reading for that too.
As for height - stick to the one in your passport? As that is probably the one that measured your spine in all its glory, upright, etc etc.