What works for me is allowing the body to move as it wishes, while I maintain a still mind, which is inclined to depth. What I observe is a gentle oscillation of my torso and head, which I have spent many hours observing, and noticed that this oscillation is a product of the pumping of blood in my major veins and arteries.
This gentle, natural oscillation of my body during deep meditation led to a rather humorous episode at a meditation retreat that was under the auspices of a guru who had no understanding of deep meditation. I was accused of having a weak mind, and booted out on the 6th or 7th day. This is what one who meditates deeply is likely to encounter in a world that is controlled by frauds.
As for going into the Immaterial Domains. It happens when you are ready. For most people it takes a great deal of preparation, because there are both demons and angels to be encountered there. Thus, one must develop deep equanimity before stepping into the spirit domain.
In between time one can work upon developing lucidity in the sleep space by journaling one's dreams. It worked for me. So, perhaps it will work for others.