Since I started taking a glycine supplement a couple of months ago, the percentage of deep sleep has increased quite a bit. Glycine is an amino acid that our bodies manufacture and is the most abundant of all. But as we age, we don't make as much. Another advantage of supplementing with this amino acid is that it is also involved in the manufacture of glutathione, a strong detoxifying agent:
www.ncbi.nlm.nih.gov
It is best to take that glycine between meals. For a better sleep, it is suggested to take it half an hour before going to bed.. I consume 1000mg on getting up in the morning with two glasses of water, and 1000mg one half hour before bedtime.
Another amino acid which helps the quality of sleep is taurine. I take some as Magnesium Taurate. Magnesium is involved in over 300 functions in our bodies. Most people are deficient of this element. I take 200mg of this Magnesium Taurate 45 minutes before going to bed. This has also helped increasing the percentage of my deep sleep. You can find interesting info on web about both magnesium and taurine.
The advantage with both glycine and taurine is that they are safe and will not cause addiction. There is no risk in trying them. If you do, I would appreciate receiving some feedback.