I have severe sleep issues and have tried a bunch of sleep related supplements and medications. Although I do not have a dietary deficiency Magnesium might be the single most effective for me at keeping me asleep, although it does nothing to help me get to sleep and unfortunately the most effective dose taking magnesium alone is around 500mg which is enough to make me even more tired than usual the next day (so not really a good option on its own for me). I have found a combination of 250mg magnesium (carbonate or extended release oxide + citrate, which seem to work equivalently in my limited testing other than that the scoop I have for the carbonate powder is for 350mg so I might take somewhat more in that form) and 2.5mg baclofen to work better than either at higher doses alone (baclofen in higher amounts quickly stops working when taking it multiple days). Unfortunately sleep issues of any severity are often fairly random so it takes quite a while to have any confidence that something is actually helping even if it seems to at first; magnesium is one of the very few that seem to help me.
I have recently been taking those with .3mg DR melatonin and 8-9mg diphenhydramine and it still has some effect the next day but much less than the higer doses of magnesium. The diphenhydramine is for my Non-24 and does not help me sleep but can improve my functioning some the next day when part of my body wants to be sleeping during the day (unfortunately like many things it seems to quickly lose effectiveness so I am going to try taking it less often). My thinking is that for long term use for sleep it is imporant that the medication or supplement be cleared from the body quickly, though too early and it may be hard to stay asleep.
Sleep doctors have told me that waking up at the same time every day is most important. It doesn't look like the paper tried to differentiate between irregularity waking up and irregularity going to sleep but I suspect trying to wake up as close to the same time every day as you can reasonable manage is the best thing most people can do to improve their sleep quality (getting to sleep earlier some days if needed). My sense is that the most obvious part of what we consider to be sleep quality is actually waking up quality. Sleep deprivation affects memory in subtle and eventually not so subtle ways but not feeling awake seems in my experience to be based on how waking up happens and sleeping less when relatively well rested often has a positive effect on feeling awake (at least for a while, getting tired early is another effect of not sleeping enough). There is a particular thing that I notice maybe a couple of times a year that feels like rapidly cycling between being asleep and awake multiple times when I am waking up and I always feel much more awake the day it happens.