Hi All... I've been watching countless videos on making a cast WBO over an exercise ball. I like the idea, because it has to be small and mobile. I plan on making a base on casters. There are so many different ways of doing it, I guess I'm looking for help on 2 things. 1) A good / proven how too, and 2) material list (preferably available in Canada). I can get my hands on castable refractory cement, but I'm not entirely sure what type of aggregate / stone to add in, or other items needed.

here's an example of one how too in the UK. https://www.youtube.com/watch?v=-j25Z65eaYk

Any help is greatly appreciated.