I still feel amused that many people advocate the technique of mindfulness for sleep. The thing you should know before practising it is, you are not getting quality sleep because your head is full of nonsense. Have you ever observed how much unconscious data goes into our mind daily, either from surfing social media, Flixing or any other entertainment source?
So as we can see, we can't much control what goes into our system as we live in a kind of virtual world.
So the only thing we could do is to put our thoughts aside. Whether they are positive or negative, just putting them aside before we sleep will help us get quality sleep.