Just get one (or two).
These are great. I purchased two. I have one in my office chair. It helps greatly to stretch my back and keep my shoulders back while using my computer. I also bought one for my inversion table. Something similar came with the inversion table but it did not last very long (was made differently and used a fabric strap rather than rigid plastic). This is much more sturdy than the one I had. I am about 200 pounds and this unit has no issues when I use it on the ground for a good back stretch.
Rating: 5 stars