@elduvelle I can highly recommend a standing desk. Mine has a pneumatic lifting mechanism, which I like for the simplicity. No trailing cable, no plug, no electricity.

I also recommend an absorbent anti-fatigue standing mat (not sure what the proper name is). I was given one and it seemed like any old mat so I was surprised by the difference it makes. Just a small square with its few millimetres of padding, but it makes a huge difference on the legs and body when standing for longer periods.