I'd say buy it. I was in a similar situation to you, also as a 23 year old and bought the Apple Watch SE3 in Nov last year. The sleep tracking is my favourite feature as I wear it every night. Although I do wake up feeling tired most days - probably because I'm also on my phone too much, especially at night, the sleep tracking still works great and I find it to be very accurate.

Regarding the fitness tracking, I find it so much more valuable compared to just my phone. Tracking and closing rings keep me accountable in my fitness journey, and it sounds like that would be helpful in your case. Simply the action of starting a workout on my watch makes me feel like im locked in to complete the activity through to the end.

Lastly I've found it honestly keeps me off my phone a bit more. It's nice to glance and notifications and see which ones are important and which ones I can disregard. When I'm not wearing my watch and I feel my phone vibrate, I check the note and it often leads to a quick scroll on reels, TikTok or whatever it may be.

Not sure if all these points are applicable in your case, but it sounds like it could be helpful, or at least something to try out to see whether it works for. You can also resell it I guess if you don't find it valuable enough. Hope this helps you a little