Not to split hairs, but I know a number of people that probably have about $30M and therefore qualify as a UHNWI. Thing is, they are pretty simple people. Sure, their house is bigger and their life a little more comfortable, but as strange as it sounds, I just don't think $30M is enough to live like the ultra wealthy. The ones I know are CEO's for good size organizations that get paid in the $3M to $5M range and of course, that adds up nicely over the course of a career. They usually belong to a country club, fly first class, eat and drink well and have a very comfortable life. But, they are basically working people in that they go to work every day and run their companies, sit on boards and are involved in their communities. The couple of people in this category that I know real well would fit on this forum nicely. They worked their way up, lived below their means and saved a hell of a lot of money. That LBYM's personality just doesn't change all that much even when you have a lot of money.
I have no idea where a better place to draw the line is, but for the owning a yacht or jet or having multiple residences in multiple countries, I think you need more than $30M. Especially if you're thinking a large yacht with a crew, a jet on call and large staffed residents in multiple countries. That takes serious coin that even those I know of would be a bit envious of.
The great thing is that it is absolutely true that you can be happy at any level (acknowledging that one may have to get to a level beyond sustenance). And if you're not, it's also true that except for a couple people on earth, there's always someone who has more than you, so you're never likely to be happy. Thankfully, I'm happy and most of all grateful for how things have ended up so far.