The best way to ensure that the pasta holds up is to cook it separately from the soup and add it to the hot soup just before service. If you do that each time you serve the soup, it will always be fresh and "new," and not like leftovers.
Otherwise, no matter what pasta you use, it will eventually fall apart and/or get mushy.
I cook my pasta seperately and put a little in each bowl and pour my matzo chicken soup over it. Orzo and little shells work good this way. No mush!