For reducing energy use, social values matter at least as much as technology. Imagine if we had no better technology - but most people drove small cars instead of large SUV's and trucks, and jet plane trips were not routine for hundreds of millions of people.
> and jet plane trips were not routine for hundreds of millions of people
So lower standards of living.
Feel free to live in a modest-sized, well-insulated version of the https://en.wikipedia.org/wiki/The_Breakers with a live-in domestic staff serving your meals on solid gold plates.
Or is your definition of luxury "performative wasting of energy"? If so, the lower the tech that you have access to, the better for the rest of humanity. :(