Sewing chairs need to be adjustable in height and have good back support. You should be able to sit directly in front of the machine needle and sit with your feet flat on the floor. If you are bending your back when you sew, your chair height is too high. Chairs that swivel and have rollers add convenience.
Stools are great for working at higher surfaces, such as ironing boards and the cutting table. To get the right height, use an adjustable stool or buy one with wooden legs and cut to the right height for you.