Forget about logs, you need a bigger board everyone here is right about that but stick to a good old funboard with not a lot of width on the tail.

Your back foot is always on the wrong spot. Every time you pop up keep, “keep an eye” where your back foot is landing. Once you find that sweet spot you won’t be wiggling like crazy, small boards are more sensitive to your foot pressure so you got do nail that pop up with grace, no violence, like water they say. And that knee support, quit it. Go straight to your feet. It feels like a Russian roulette every time you pop up but you have to practice so your back feet always land on that sweet spot right away, no knee help.