simpleas,
It is common for us to see death linked to suffering as that is normal take cancer for as an example, but the phrase “less you die” did not have to be associated with suffering. Of course it very well might have been.
Before Satan entered into the garden in a physical form, we do not know how much time had passed from the moment God breathed life into Adam and Eve was created from Adam. The time period was long enough for Adam to not be influenced by concupiscence as he was able to see perfectly the nature of animals as to name them. The idea that he named them is meant to reveal that Adam named an animal according to their nature. You could not do that with a weakened intellect ( no concupiscence at this time). To have dominion over something begins to knowing who you are dealing with and is also the formula we see for exorcisms. See Gospel accounts when demons ask for Jesus name and Jesus responds by knowing the demons. A exorcism counter exorcism. That side note is just to quickly provide a deeper understanding of what is meant by naming and having control.
Adam and Eve never ate from the tree of knowledge of good and evil when there was no alien threat to do so. It only came about when Satan entered into the garden and threatened their life by revealing to Adam and Eve if they do not eat of the tree, in a cloaked way, they will be punished. Of course God would not punish Adam and Eve for not eating of the tree after all they are rewarded with paradise. The language used to describe Satan in that setting is the same language used in the book of Revelation, so a beastly dragon. That is why I am saying they feared suffering at the hands of this unknown powerful creature before them. A creature though they did not name they surely knew his nature, and probably even the fact that he is not a respecter of persons and life, and though God would raise them up; they also knew God would did not have to intervene in their suffering by this creature. If God did not prevent and stop the fall of his highest Angel and others God most likely would not prevent Satan from harming the physical body of Adam and Eve. Of course Satan or no man has power over the soul.
If Satan would not have appeared in a physical form the threat would not have been there.