I use an armless office chair. It swivels, height is adjustable and so is the slant of the back. I rolled up an old towel, used masking tape to secure it around, then looped a bunji cord through this roll. I fastened this to the back of the chair using the bunji cord.
A physical therapist told me to save $... use a rolled up towel to support the lower back. My contraption might not be the best looking but my lower back is supported.