No, you don't need expensive chairs for coding, you don't need to "sit down well" because it is not possible or good for you. Do sit for hours in a "correct" posture and you will discover that your body tries to move constantly from it (blood circulation needs your pressure points to change constantly or bruises will appear).
Instead of buying expensive things go buy experts book on the area of posture, or better, go talk with expert people in the field. Books like this helped me in the past(I had pain in my back years ago) :
http://www.amazon.com/Steps-Pain-Free-Back-Solutions-Shoulde...
But I assert you that in the area you live there is already lots of good people that could help you. In my area I found a martial arts expert(that won Olympic gold medals when young) that could identify wrong postures from an eye shot.
PS: I code mostly standing up and with a high stool.
Instead of buying expensive things go buy experts book on the area of posture, or better, go talk with expert people in the field. Books like this helped me in the past(I had pain in my back years ago) : http://www.amazon.com/Steps-Pain-Free-Back-Solutions-Shoulde...
But I assert you that in the area you live there is already lots of good people that could help you. In my area I found a martial arts expert(that won Olympic gold medals when young) that could identify wrong postures from an eye shot.
PS: I code mostly standing up and with a high stool.