So, I decided to build my own. I still need to sand and paint it, but here is our step stool for the T@B.
We used a 2x10x8 board. The platform is two pieces of 2x10x2, and the verticals were made by cutting the remaining 2x10x4 into two pieces on a diagonal. Then I got some right angle braces and a scrap piece of 2x4 to make it good and sturdy. I also placed a piece of outdoor carpet on the top screwed down with some washers to keep the screws from pulling through the fabric.