I understand your dilemma: plus-size clothes are wider AND longer than smaller sizes, so folding and fitting in the suitcase is a problem.
First go to the Dollar store and buy several packages of white tissue paper. Make sure it's white; the colored tissue can run.
You fold using a modified "man's shirt" fold:
Lay the garment flat and face down. Put enough tissue paper to cover the back. Fold lengthwise (this is the tricky part) so the FRONT lays naturally with the collar showing. No weird folds, etc.
The outer edges should meet in the back with the tissue inside, maybe overlap depending on the size of the garment.
Then fold the sleeves back, and if they are long, put some more tissue in.
Then fold another piece of tissue lengthwise and put it on the back of the garment where the edges meet. Then fold it lengthwise over the tissue. You may have to do a little extra fold at the bottom, then fold over again, depending on the suitcase.
Crisscross or end-to-end the garments, so all the collar (thicker) ends are not stacked together.
Pants can be packed with the little extra fold at the top, and then another fold over to make them fit. Use tissue depending on the fabric.
Too much info????