I had that problem. Even 9 hours wouldn't rest me, as I wasn't getting quality sleep. Went to an ENT, who scheduled a sleep study. I have sleep apnea. Got a CPAP (on my third now, 14 years later). Since then, I'm fully charged with 6.5 hours of sleep. Consider a sleep study.

Caffeine after ~3pm is a no-go for me (other friends of mine have different cutoff times)

Also don't forget that alcohol can make sleep lower quality as well.

Working out regularly also helps, as well as avoiding screens for 1 hours before bed.