Weird advice, I know, but if you can make a space that is barrier free and safe for walking, try moving more as you read. It takes some practice and you definitely move and read slower, but I started reading and pacing (backwards, even!) and it really helped me.

You can also try a deep squat, holding your knees with one hand and a book in the other. Again, it's very short term, but changing positions regularly is so much better for you than just a supportive chair.

Recently, I've just been setting an alarm on my phone each hour or 90 minutes to do 30-40 pushups. I have to stop what I'm doing, sure, but it makes me feel less hunched and sore at the end of the day.