Thank you for your answers.

I know (I am aware) that I have to get up once in a while (I was told minimium once in hour, ok you say twice in hour) so I have made task scheduler so it pops up every hour to remind me (I might change it to 30 minutes now) to get up and sometimes I do, but usually I don't, but I will try to work on that to make it my habit (i mean you can work on your computer standing just as you can do sitting).

And you said you had to look after your posture all your life, not to relax your back but to keep it straight, so if I may ask you one more question.

I have started taking care of my posture maybe 2 months ago and I do come with the attitude to keep my back straight but I quickly loose focus and forget about it and my back is, just as you said, relaxed 9/10 of the time. So I wonder after years of taking care of your posture does it comes automatically to you so you don't have to think about it (you just do it automatically), or you still have to be focused on your posture all the time (just as I do)?

Thanks, all the best!