Smallest/simplest change possible with maximum benefits

"Mehr Licht!", as Goethe would say. Lighting is very important and it's one of the best bang for the buck things you can do.

Good pens. I always buy pens and experiment with different types. Every pen has a certain flow and friction required to deliver ink. For people who don't write a lot, this is unimportant. If you write a lot, it becomes palpable. Does the pen just roll and write, or does it need to be "pressed" and "pushed" to deliver ink. Does it dry quickly? Does it "shit itself" and smudge: when you trace a line, by the time you get to the end of the line, did the pen deliver more ink than necessary to trace a line and form a sort of drop around the tip? It will be messy. You have to clean it on a sheet of paper or that ink will find its way on the next thing you'll write. Does the ink stick well and survive a drop of water or a tear for example : )

Good notebooks: are the squares small and noisy? Do you use the same pen color as the notebook lines which makes it harder to read?

A good headset. I record our video calls and I used to have a Bluetooth headset, which meant I couldn't use the microphone (I'm on Linux). We bought another type of "wireless" headsets where you plug a dongle (SteelSeries Arctis 1). They're cheap, but now I'm recording from my headset's microphone, not from my laptop's. Which means the noise of the fans doesn't make it to the recording. The fans are really noisy (when you do Jitsi + OBS for recording).

At age 20 I decided to no longer add sugar or salt to foods and to avoid consuming saturated fats. This was based on news reports stating the overuse of these items in processed foods. I consider giving up sugar to be one of the best decisions I ever made and recommend it to you.

I'm 30 now and my best small changes were:

* Walk more - Getting a Fitbit motivated me a lot

* Sleep better - educate yourself about sleep

* Write things down - I refer to this as a superpower.

Smile.

It has mood altering effects in our own bodies, and other people respond very well to it.

I know you mentioned exercise, but it doesn't have to be a huge commitment.

I try to bike 30 mins a day. Pre-covid, that meant biking to work and back. (I'm lucky to live close to work.) These days, I take off for a 5 mile ride around lunch.

That half-hour helps stabilize my mood, and refines my focus the rest of the day. Tying the change to a daily routine (like commuting) makes it easier to stick to.

Also, changes of scenery. Especially right now, it's easy to feel trapped at home. Going for a bike ride or driving out to the woods occasionally helps my balance.

Wear sleep mask to ensure light doesn't degrade your sleep. It must be comfortable and not move around when you're sleeping. So a silk one is better than the thicker ones sold as travel sleep masks.

Just do something each day. Streaks are powerful motivators. Read one page. Do a single push up. Message one friend to see how they're doing.

I quit smoking and drinking alcohol a long time ago. It's the best thing you can do to improve your health.

Walking 2k a day, eating less bread, milk and butter.

I would recommend obsessing over your hobbies until they become a profession.