Don't nap longer than 30 minutes, it'll mess with your cicardian rhythm and make it harder to sleep at night.
Also sleep has roughly 1.5 hour cycles, if you sleep any multitude of that (like 6, 7.5 or 9 hours) you'll probably feel okay regardless of if you got enough sleep. Too little will catch up with you later.
I have an overactive mind, AD(H)D and anxiety, so I can take hours before falling asleep and I've had serious problems with unsomnia in the past. But I've got meds now that help me regulate and I've never felt better. It's allowed me to generally get 7.5 hours on weekdays and 9 hours on weekends.