Nicholas Flanders began thinking deeply about his sleep a few years ago when Twelve, the carbon-transformation company hed co-founded in the Bay Area, was in the midst of funding rounds. The stresswas having an impact on my sleep, he said. He sought out fixes.Today, Flanders, whos in his 30s, has an impressive sleep stackthe term for the set of tools and tech that obsessives use to optimize sleep. His mattress cover changes temperature throughout the night. His Oura Ring 4 tracks sleep stages.