Stage 4 NREM sleep ("deep sleep") correlates strongly with feeling fresh. However, a proper structure of sleep is also vital. To get lots of Stage 4 NREM: adhere to your circadian rhythm, exercise, and avoid NREM-suppressing medication.

Although you get lots of NREM early in sleep, cutting down your sleep with alarm clock will likely take away all freshness as soon as the homeostatic sleepiness kicks in.

For that reason, you should sleep as much as your body wants to
Any suggestions?