Ergonomic, comfortable office chair

I would rather recommend a height-adjustable desk so that you can also stand while working. As a change from the chair, try using a stability ball occasionally. Sitting on a chair is still sitting on a chair, even with a really good chair. And sitting on a chair is ergonomically harmful. A good chair only helps to a limited extent.

p.s. when it comes to the "back," definitely stretch the "hamstrings." Practice squatting without lifting your heels off the ground and try sleeping on your back, with no pillow or just a low pillow.

I am also looking …. I have already looked so much, I just can't decide … it should also be nice

Sedus, Vitra, Steelcase - you can take all of them as a brand. They are not much different. Try them out and sit down for a test.

In the office, we have a Sedus schlag mich tot. In the home office, I sit on a Steelcase Please V2. Both are equally comfortable. The Steelcase cost about €600.

Then a really dumb question: where do you go to test it, do the regular furniture stores have it in their assortment?

No, you usually don't go there. In larger cities, there are always office supply stores; you go there, test the chairs, and ideally go back again two weeks later to test them once more. And if you find the same chairs comfortable and good on both occasions, then you have found YOUR office chair. I also recommend the company Dauphin.

I am extremely satisfied with my Herman Miller Aeron. My wife swears by her Vitra Physix, but for me the backrest is too low in the long run.