Curie is a personal trainer that will coach you to sit better. It's not about sitting straight all day but taking quick breaks and simple exercises.
Plexus Wheel Plus is the World's Simplest Back Relief
The Posture Laptop Stand is designed specifically for hotdeskers - those of us who need some neck re-alignment while we work, but have to pack up and run at the end of the day! Posture is super lightweight and portable.