I'd say anything that engages the core (superman, plank variations) and activates the upper back (YTWL's) would be good choices, ideally substituted with some stretches or mobility work
How long are you using it for every day?
I also own that chair, but i find it uncomfortable for longer periods of time and tend switch to a chair with a backrest after ~1h
The argument could be made that if you do not have 10+ years to wait, you should not be investing large amounts in the stock market at any time. So now would probably even be a good time to do so, but of course, nobody knows.
I'd say anything that engages the core (superman, plank variations) and activates the upper back (YTWL's) would be good choices, ideally substituted with some stretches or mobility work