I dont think I have back pain yet. I feel it some times when i focus on it.
I dont have a big space but I can easily switch my setup standing-sitting.
I dont have space for treadmill either but my work allows me to take 20mins break easily every hour or so. I plan on walking for 10-20min wherever i find myself.
from comments seems like kobo is right answer. i can also endorse i have both kindle nd kobo, things are simple with kobo