If your office chair seating is not comfortable I would recommend getting a purple seat cushion to place underneath your bottom.
I sit for hours at my home office chair sometimes when I'm blogging or doing other work and my office chair used to cause my butt to hurt.
I got one of those purple seat cushions and now sit on the purple seat cushion and my office chair is much more comfortable.
I also added another purple seat cushion to my back as well which helps me be more comfortable in the office chair.
Or you can get some memory foam seat cushions as well and those too are comfortable but I prefer the purple seat cushion.
Also try adjusting the height of the office chair and make sure your feet are resting on the floor with your knees straight out and not up too high and sit back in the office chair instead of leaning forward.