I used to work in an office. As a CMO I spent, of course, about 12 hours a day in front of my computer. With a not-so-bad office chair, a big table and lots of non-ergonomic things and attitudes. I had back pain, but definitely not as I have now that I've started working from home.
About 8 months ago I was not even thinking to become a developer. I was only a computer-and-internet-addict. So my home was just equipped with little corner desk with a fancy decorative Ikea chair and only one 17" laptop which was not even connected all the time.
So the following day I quit my job and started spending the same 12 hours in front of my computer I found out that my work/study station was far from being ideal, healthy or even comfortable.
And, hey! I had just quit my job and the payroll, so I couldn't invest pretty much money on changing stuff and equipment.
So, 6 months later, this is what I've learnt about the most necessary adaptations for my desk right now.
I tried to improve my posture a bit by being more conscious about how I sit and even adding a pillow in the lower back area. And a cardboard box to rest my feet. Nothing actually helped in the long-term.
From ALL the things I can recommend, THIS is actually the most important one.
In the end, back and shoulder pain will end up by pulling you apart from work and focus.
After long research, I've gone for a mid-price gaming chair. These are designed to spend about 24 hs playing videogames, so It must work with a bunch of lines of code, right?
High back rest, full of cushions, pretty flexible... I was able to find good offers from €100.
I must admit that I've never seen the double screen as necessary as I do now that I code.
Code comparing, testing, and just having a big screen that helps you read easier than a 14" is reaaaally helpful.
Not compulsory, but It makes a difference.
I am sorry I am not the vampire-kind developer. I need light, and I need it to be controlled.
And when I say controlled I mean: no reflection on the screens, no shadows, and of course, WHITE LIGHT!
I have the room light, but I also found quite useful a desk LED white light. It helps my eyes a lot.
I moved to laptops a long time ago and must admit that I love the laptop keyboard. But for long hours of coding, and especially If you set up a double screen, having a keyboard and mouse separated from the laptop helps a lot to be more comfortable and rested.
As I love the soft flat laptop keyboards, I bought the one I found most similar to it for a reasonable price (about € 30):
HP Pavilion 300 (Wired) and HP mouse too. I didn't want to struggle with batteries.
If you are using a laptop, a computer elevator will also be helpful. Since it places the screen closer to your sightline it will improve the way you sit and neck rest.
A foot rester will also help your legs to have better blood circulation and best sitting posture.
A yoga fit-ball. These balls are great for general exercise and to stretch your back. And of course, it is extremely fun to bounce on it and try to roll on it (heheehe). However, it is not very recommended as a sit (see these therapists for more info).
From here on, you can invest in lots and lots of amazing stuff, but I found these to be the basic equipment to feel minimum comfortable and take care of your health.