Office Chairs?

Hi everyone! I'm 20 weeks and have an 8am-5pm office job. Getting increasingly uncomfortable in my chair - bump aches if I don't walk around every 45mins or so, which is pretty inconvenient. Feels like my lower bump is being restricted by my own legs now that it's big enough to rest on top of them :-( Do any of you have the same problem at work? If so, what has helped? Also, does anyone know if kneeling chairs are recommended for us preggos? I like the idea of them but not sure if they're suitable...