A sure-fire way to increase your happiness is to work out. Do 40 pushups a day for a week, see how your mood improves. Your body is meant to be exercised, don't deprive it of movement and muscle ache.
When I used to go to the gym I remember always sleeping soundly, always waking up feeling awesome and always having a great feeling throughout the day. Can't recommend it enough.
And if you can't do 40, do five. And if you can't do straight pushups, do knee pushups. And if you can't do five, do one. Then two. Then five. Then 40. But don't rush it, just do what you can and then a little more.
Seconded. People often get overwhelmed at the scope of "become more fit" once they've finished a workout or two. Doing it one small accomplishable bit at a time is a totally valid way of building a fitness habit, and is NOT something to be ashamed of. And for the RPG nerds here this is exactly how you level-up IRL.
In my personal experience I did 40 pushups every other day for months and my fitness level and happiness did not noticeably increase. Also did curls, tricep moves with 25 lb dumbbell. And crunches.
Then I got a weight set where I could progressively add weight every week. And ate more and had appetite. That finally made a difference in fitness level and mood.
Bodyweight exercises can be made progressively more difficult, too; it's just that it's not quite as obvious how to do it. But there's definitely a mindset that a pushup is a pushup is a pushup, which is sort of limiting. There are a number of programs out there that offer stepped progressions for bodyweight exercises that provide a similar ladder to freeweight work (working, for example, from knee pushups through, eventually, to one-armed pushups). Not saying that's the right way to go for everyone, but the barrier to entry for bodyweight exercises is satisfyingly low, and for some people, not having the excuse of "I can't exercise because I can't go to the gym" and/or "I can't exercise because I don't have X equipment" is a net win.
Yes you can do a bare minimum but without progress you may lose motivation. After a while you get used to the slightly better feeling and slightly better sleep. May get bored with it only to go back to the occasional workout. That was me. I needed a more noticeable result.
Progressing to complex bodyweight exercises is trickier. Lifting weights properly is technical enough, planche, even headstand pushups weren't going to happen for me. I made every form mistake you can make with weights. Mistakes with complex bodyweight moves halt progress.
I started last year doing 5 pushups first thing when I got to work in the morning. Now I do 50 pushups every morning.
If your office has treadmill desks, use them! I swear I get more coding done on the treadmill than I do sitting at my desk. (it could also be the fact that fewer people bother me on the treadmill.)
I started doing the seven-minute workout before I showered and ate breakfast in the morning and it improves my day immeasurably. Getting the juices flowing as soon as possible is quick, easy, and wonderful.
When I used to go to the gym I remember always sleeping soundly, always waking up feeling awesome and always having a great feeling throughout the day. Can't recommend it enough.