The difference in weight from the live body vs. its corpse can be explained by natural means. I doubt that weight change reflects soul.
The Good News:
The Soul itself cannot at this time be isolated from Mind. Mind, fortunately, has had tons of research delving into it, so its existence as separate and apart from the brain has been shown. I'm sure you've heard of out-of-body experiences and near-death experiences. It's pretty persuasive that people, blind from birth, can describe the colors, objects, movements, etc. "seen" while the brain was incapacitated during surgery or a life-threatening event. To fully understand all that Mind can do in the here and now, from long-distance viewing to affecting the physical world, you should read Your Eternal Self by R. Craig Hogan. To show that Mind transcends death, the book The Afterlife Experiments by Gary E. Schwartz is based upon experiments conducted to scientific standards at the U. of Arizona. Both are on Kindle and there are many, many other books dealing with near-death experiences and transcending death...you can break the bank on Kindle on these two topics alone...but the two I mentioned are a good starting platform.
Since the Mind is eternal, that should prompt curiosity as to reincarnation. Again, there are tons of books about this, but the best starter-offer is Born Again...by Dr. Walter Semkiw. He is continuing the multi-decades work by Dr. Ian Stevenson, now deceased, so any of Dr. Stevenson's books are also very reputable. Just as fascinating are books by Dr. Brian L. Weiss, whose string of credentials is way too long for here. Like most psychiatrists who use hypnosis, he stumbled into past lives; I think Many Lives, Many Masters is the first book he wrote about his sessions.
The Bad News:
It's just about impossible to describe Soul in earthly terms because it only becomes tangible in its native environment.
So...to get closer to your original question....each human possesses Mind. Mind is influenced by two forces, the brain (phenomenally puny) and the Soul (which so far we can only express via Mind). The brain will someday perish, but all its thoughts and emotions will have been recorded on Mind to turn up over and over.
Why don't I simply accept Mind as Soul? Because one afternoon when I was 17, I lay down for a nap and woke up in another reality (and I wasn't near death!) and I experienced Mind and Soul as different entities. So that's my truth, but it's hard for others to accept it. If you can't, just use Mind and Soul interchangeably.
You ask about Soul. Yes, it feels/is completely physical in its natural realm. You can feel its energy, see its light, experience its frequency. It's very physical, but only in the place/dimension where its nature is the real world. There it has substance. Here, not so much. Mind stays with it, but I was able to project my Mind outside of my Soul to see elsewhere and check out the new environment. That's how I know the two are not the same. It is the quality of the Soul which determines how close you can get to the Source (God, Christianity's Father). Mind helps improve the Soul's quality and here on earth the brain can help the Mind with this task.
Christianity sometimes describes the Soul and the Source as light, more often as son and father. If people would get past understanding Christianity at the literal level (which is strange because Jesus indicated that his profound truths were well hidden in parables...and I assure you, they're very well hidden...not at all what a Sunday school class comes up with), they would see that Jesus' teachings are all about the primacy of eternity/Soul over the material world, how to upgrade one's Soul quality in order to escape reincarnation, karma...there's a treasury hidden in the Synoptics that no one knows about!
I don't know that this helps...read the books I suggested.
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