Have style, not a lifestyle
I briefly worked with a senior technical manager whose wife also worked for the same company, but at a different site. They'd bought a house about halfway in between, but they both had long commutes. When I mentioned that my wife didn't have a regular job, he said, "I wish I could do that, but I need the second income to support my lifestyle."
When I got home that evening I told my wife, "I'm sure glad I only have to support us and not a lifestyle too."
When you get to the point that you start talking about your lifestyle as if it were an additional member of the household, you're far, far gone.
Avoid having a lifestyle. But that does not mean not having style. In fact, having style is very important. Having style is how you resist the dreaded Diderot effect.
You can't read very many articles on simple living without running into Diderot and his effect. Denis Diderot was a French writer who wrote a famous essay "Regrets for My Old Dressing Gown," in which he describes how a handsome new dressing gown that he received as a gift was so nice his other furnishings no longer seemed to match it. He ended up buying all new--a leather chair to replace his straw one, a desk to replace his table, new pictures, new clock, new bureau.
The essay is famous not only among advocates of simple living, but also among advertisers who yearn to trigger the Diderot effect in every buyer. If they can but get you to buy one nice thing that makes everything else you own seem shabby, then they can get you, like Diderot, to upgrade everything.
The key to resisting the Diderot effect is to have style. Not just any old style, but a particular style. Something nicer than everything else you own isn't in keeping with your style and that makes it easier to resist: It's just not you.
If, despite your efforts, you do end up with one very nice thing, think of it as special and not a reason to upgrade your other stuff. After all, there's nothing wrong with having a very nice thing.
It's fascinating to watch how advertisers try to suck you in. They know the power of the Diderot effect, and the way it affects not only you, but all your neighbors as well. Not only you will want more nice stuff, but all your neighbors will need to upgrade their things as well, just to keep up.
You can thwart them, though, if you have style.