The bottom line
Supplements are potentially even more interesting for sleep than they are for pain. That’s because there are only a small number of pharmaceuticals for sleep, and many don’t do well on these.
The most basic supplement for sleep is melatonin, but there are many others to consider. Melatonin supplementation is largely unnecessary if you are able to darken your room lighting enough to produce your own melatonin.
Racing thoughts is a major impediment to sleep (other than pain, of course!). Thus, anti-anxiety strategies can also help with sleep.