If your ladder is too sturdy to kick over, kick away from you, or even slide away from you (and I would really double check to make sure this is actually the case), then I would use a chair or a stool instead of a ladder. Most ropes are long enough to adjust the height of the noose, even if your anchor point is high up. I would adjust the height of your noose so that you can fit your neck into it when standing on a chair or stool. If your rope isn't long enough to do this, I would buy a longer rope, which is usually very cheap and easily accessible.
It may not be the most satisfying answer, but you need to be able to kick away your platform when doing full suspension if you want to be 100% sure it'll work. And if you can't do that with your current materials, you need to acquire new materials. Best of luck on your journey, wherever it takes you