My sleep is OK — how do I make it actually reliable?

Your sleep is adequate and you want it reliable. This is the right time to work on it. Sleep is easiest to steady before it becomes a crisis, because the anxiety about sleeping has not yet become the thing keeping you awake. First, fix the waking time, not the bedtime. This is the reverse of what most people attempt. The body sets its rhythm from light and from the hour you rise. A constant waking hour draws the rest into place over two weeks. A constant bedtime, with a scattered morning, does very little. Second, take light into the eyes early. Outdoors, within an hour of waking, for ten minutes. This is the strongest of the levers and it costs nothing. Third, give the body one short sequence that means the day has ended. The content matters less than the repetition. The body learns sequences, which is the whole basis of practice. Fourth, leave the bed when you have been awake some twenty minutes. Lying awake teaches the body that the bed is a place for waking. Rise, keep the light low, return when sleep is near. Fifth, hold all of this during the untroubled weeks. What is practised only in difficulty is not practice; it is rescue. Steadiness is built when nothing is wrong, and it is there, already built, on the night you need it.