A lot of times when I play double bass, I find myself trying to keep the double bass steady. After some research I did, I found out that I need to balance it against my body. How do I do that? Every time I try, the bass slides to side.
It is much easier to balance the bass sitting on a stool than it is standing. When on a stool, you can take your left hand entirely off the bass without it sliding; but when standing, I have found that a small amount of the bass's weight will always be on the thumb of your left hand. For this reason I always prefer sitting to standing, but it's possible to have most of the weight on your body when standing also.
The main thing is to let the upper bout of the bass rest on the left side of your crotch area, between your left leg and your stomach. The bass should be standing mostly straight up, tilted slightly towards you. If it is tilted to much in any direction, it will not stand still without left hand support. Also, you may have to raise or lower your endpin to get the bass to rest correctly.
You can play around with different angles and positions of the bass to see what works for you.
Sitting is much easier because you can prop your left leg up on the stool, so that your left knee sticks out and the bass rests against it.
I have also found that when I play sitting down, my bass usually rests closer to the right side of my crotch rather than the left side.
Sitting is much easier than standing, as has already been pointed out.
One tip if you must stand is to raise the toe of your left foot so that the bottom of the bass to the left of the spike rests against the tip of your shoe. (The spike will have to be fairly short for your foot to be able to reach.) I find that if I do this then the bass remains steady even when I take both hands off it. Make sure there is no chance of the spike slipping on the floor if you are going to try this.
Try experimenting with different positions, and find what works best for you.