When I was doing a long period of intense yoga training, many years ago, we would do surya namaskara (salute to the sun), at least 6 days a week. No stretch & use-correct-posture type surya namaskara, it was just about getting it done.
We used dynamic surya namaskara with the deep lunge variation, you take one leg back into a lunge, & at the end of the moves, you are also bringing a leg forward into a deep lunge. This makes a 1/2 round. The lunges use the other leg for the next 1/2 of a round, so 2 namaskaras alternating legs for the lunges, are making one round.
An easy version is here, another here
And when you are doing 10, 27, 54 rounds each day, it's a real effort. Forget slow breathing, perfect form, etc. Just do it! Especially when 10 rounds, as described above, should only take us 10 minutes. I still prefer this way. It creates an energy, is highly beneficial to our endocrine & nervous systems, & is quite aerobic. It made us all very supple, & surprisingly strong. Any exercise similar to a squat, in this case it's the kneeling lunges, greatly improves overall muscle tone. And all those mountain poses/down dogs, give a lot of upper body strength.
It's not the only way to so surya namaskara, of course. I know a lot of people doing the Mysore style surya namaskaras A & B. 2-3 of each is a good early morning routine, & they are done more slowly. A nice little variation is by Mandy Ingber. Any salutes are hard to do at first, but Mandy does do a nice one.
If you add a twist....any sort, whether dynamic or holding one, easy or harder, plus either the bridge pose, or 1/2 shoulderstand will round out an early morning practice.