The thing that finally worked for me was blackout curtains in my room. I didn't realize just how much the incoming light from outside my window was affecting my sleep. In pitch black darkness, I'm out like a light and have the deepest sleep imaginable. (It's so effective that I have to set an alarm to wake myself up, otherwise I'll stay asleep for 10-12 hours)

I'm able to replicate this somewhat using a sleeping mask, but I find most of them pretty uncomfortable; I like to sleep on my side, and that doesn't work terribly well when something's on my face.

Full disclosure here of course, I work an evening shift (12pm-11pm) so I'm used to going to sleep much later in the evening. Even still, I often found difficulty falling asleep due to light bleed from the lights around my apartment, and I feel like this contributed to my sleeping issues more than the sunlight in the morning, which my body's clock seems to have adjusted to on its own. (I still naturally wake up around 10-11am even without blackout curtains.)