Try floor sitting. It's not perfect in the summer months since you get less airflow around the legs, but it lets you move a little and stretch as you think which is very healthy. Dozens of postures possible. It can be done cheaply, cheaper than a "normal" desk setup:

1. Folding floor desk(ideally taller and wider than a breakfast tray so there is leg room)

2. Lap desk for peripherals. This makes computer interactions ergonomic, no more hunching or reaching.

3. Floor chair/backrest so you can recline and get some back support in long sessions.

Plus all of it can fold compactly so it works well in a limited footprint.