I put a little strap from the base of the stepstool around my axle a couple weeks ago, to keep it from sliding away. It was frustrating before I did that.
I don't have one, but this tire step looks a little nicer than the one linked above. It's also cheaper and fits larger tires. https://www.amazon.com/dp/B0002Q8TW...TG&pd_rd_r=S5Z6901KXRFY6D49ZTJ5&pd_rd_w=4RaiL
This one looks promising...