I have just switched back to a nice but fairly standard office chair.
I tried the saddle stool and it felt AMAZING for my lower back, but I've had a total hip replacement and the way the saddle seat pressed against my seat bones on that side made me uncomfortable after about 15 minutes, so I couldn't keep using it.
I switched to an exercise ball for the last several months, and it was good but not perfect. I had to get a large ball to put me up high enough, but it was so big around I had a hard time sitting on top of the ball and still being able to reach things like the pedal - I would end up sitting sort of halfway rolled forward which put me too low. Plus the rubber is kind of grippy so I couldn't easily turn around to get to my design wall directly behind me, which was a big drawback for how I work. Other than that it was really comfortable.
So I'm back to an office chair. It's a better-than-average chair (and cost accordingly) - it has arms that flip up out of the way which is great, and I added a memory foam cushion to the seat so it's comfy for long sewing sessions. My room has faux wood floors so I got a low-nap commercial grade entry rug and put that under my casters and it works great - I can roll easily when I want to but there's enough resistance that I don't inadvertently roll away when I'm struggling with a big quilt, plus the floor is protected from wear.
I kept the exercise ball and put it in the living room - I sit on it to read now. It's FUN to sit on, I move and bounce around on it a lot without thinking about it, and it helps stretch my always-sore back.