+JMJ+ If you only had the slightest, true awareness of the immensity of God's mercy, you would not commit a single, fully deliberate venial sin, much less a mortal sin. Such an understanding, however, is supernatural, that is to say, we are not naturally capable of acquiring such understanding. Only by God's grace can we have such an understanding even in the slightest capacity.
You've heard it said that God does not wish anyone to go to Hell, then why does anyone end up there? People who go to Hell choose Hell --- they chose separation from God by sin. How can anyone choose Hell, or even Purgatory, for that matter? It is not enough to say to oneself, "Well, I choose Heaven, therefore, I shall go there," for with any destination, even in the life of the soul after death, it is not enough to choose any path to get to one's destination, for not all paths end up in the desired destination, or are expedient in arriving to one's intended destination within the time alloted. Since we do not know definitively, our alloted times, we must choose the expedient path to being united with God.
"How is it that one could choose a place to dwell in eternity if in death one no longer has free will?" By the moment our souls are separated from our bodies, we lose our free will.
If a person was to learn of God's infinite goodness, truth, beauty and mercy, and yet he had any stain of sin on his soul, or attachment to sin, he would be so humiliated by seeing God for Who He is, and who he is himself as a creature of God by what he has become by his choice (by his being in sin or attachment to sin), he could not chose Heaven because it would not be possible for him to will it by this knowledge of God. We cannot choose Heaven truly without having chosen to know, love and serve the one, true, Triune God in the way that He desires. (This ability to know love and serve God comes to us through Baptism, when the supernatural ability of faith, hope and charity are infused into the soul, and remains animated in the soul as long as it is in a state of grace.)