Thanks everyone for the replies, still waiting for feedback.
As a clarification: the chair cannot be exchanged, for now. The rug rarely makes contact with the chair, it's just there for looks and as a dust trap. The floors are PVC covered, those come with the building, cannot change them (as a tenant) without significant expense. They are grounded (electrical floor heating) but they still build up charge on the things that are on top of them.
Most of the static is generating when getting up from the chair. Humidity is always 40%+. In the winter is even higher (around 70%).
A wrist (hand or foot) strap can be added, but it's too inconvenient in everyday usage, as I have to get up a lot.
Other than that, I take all necessary precautions when handling electronics stuff. However, I do have visitors that sit on my chair and build up charge. I dislike having to tell everyone to discharge and 'take a shock for the good of mankind' before touching ESD-sensitive stuff.
However, I will slowly implement all of the measures mentioned so far, hope they mitigate some of the potential problems.
Questions on the suggestions so far:
Still not sure on the ion generator gadgets: how would one look for them on amazon or something similar? Do they really do something?
Anyone tried adding a dissipative brush/chain to an office chair? I have the suspicion that would work the best.
Do humidifiers add dangerous conductive salts? Do they dissipate just humidity without salts? Or are they supposed to be used with distilled water?