So we have the distinct advantage of being able to use the natural swing of our arms to play the cello, and particularly to feel the weight in the strings in our right (bow) arms. Sometimes it's hard to let go (there's a life lesson in here, huh?) but when we separate out the two main planes used getting the weight of the arm into the cello, perhaps it makes more sense to the body.
What do I mean by planes? See the illustration below. Green is the horizontal (or table) plane, purple is the horizontal (or door) plane, and red is the sagittal (or wheel) plane.
In the video, I make the point that we are playing in and around several planes at once, because the cello is at an angle to the body. If you are having trouble feeling the weight, which is both down toward the floor (on the horizontal plane) and in toward the body (on the vertical plane) you can separate out each plane to feel it individually and then put them back together with a regular posture. Once your body feels both planes individually it might have an easier time with the combination! I'll leave it to you to think about the sagittal plane!