I like to think of my physical body as just a shell.

i like to think of it that way as well,
but it was odd to realize that my body is a physical, three-dimensional object.

my science may be unsound, but i was thinking, if there is a constant amount of matter in the universe, and it cannot be created or destroyed, the matter that makes up my body would have been something else if i hadn't been conceived. i was wondering for a long time what i might have been if i hadn't become a human being.

and that in itself my body is not unlike its own universe, with living cells and "planet" organs, so to speak.

furthermore, when i die, my body will still exist as real physical matter. until it decays, at which point i'll still exist physically, but as something else entirely...

Of course. In reality you're just a big chunk of carbon and silicon and other atoms from deceased stars that has come together and developed a consciousness. It's interesting how simple yet how complicated it can be.