I wasn’t able to find your description of olam habah in the Derech Hashem. However, the Sifsei Chaim has a really interesting piece on that where he explains the ‘chad charuv’ in the elef hashishi and then he explains the purpose of the elef hashvi’i through asiri. He explains like you say (probably based on the Ramcha’l) that there will be some bechinah of gashmiyus but it becomes smaller and smaller.
The body that you are referring to is called a chalukah d’rabbanan. That is for getting around int he olam haruchni as your paper example explains as necessary.
The whole point of the Ramchal though is that in olam habah and before the cheit the guf itself would become dak like the neshama is now and the neshama becomes even more dak. To me it seems that this is what happened to Eliyahu. Since he never died he must have reached a situation of before the cheit in which case the properties of his guf would follow the laws of how the neshama was supposed to affect the guf.
The most I was able to find in the Derech Hashem was in Perek gimel sif zayin, ches and maybe tes. But that seemed to suggests more like what I was saying.