We have a heavier comforter for "winter" (this is San Diego) and an extra-lightweight down "blanket" for summer. Whichever one we are not using is stored in a pillow case on the top of our closet where nothing else would likely be anyway...on the very top of a stack of long, flat boxes that would ordinarily be under the average person's bed. LOL I prefer to have a clear space under our bed. We sleep better that way.
The winter comforter requires two king-size pillow cases. I use the jersey knit ones where we repurposed the sheets since we did not like them for sleeping. We fold the freshly aired and sun-freshened comforter (hung out on the line in the hot spring sun for several hours) as tightly as possible and cram it into one case, then push and pull and cram it the opposite way into the second case so the entire comforter is covered. This compresses it significantly and avoids plastic.
The summer down blanket fits in either two regular size pillow cases the same way or just one of the king cases above and fold the end over to discourage spiders and such.
We store all of our travel gear in our largest suitcase. Otherwise, I love that idea!