I drew a simple pattern where the basic measurements are: breast, waist, hips and length of the top, and the height of each measurement on the spine, measured from the neck vertebra.
I drew neckline 11 cm wide (half) and drew a slanted 3 cm shoulder.
I cut strips from the gigantic sleeves and used it to finish the neckline and armholes. The mesurement was 0.8 x neckline.
I sewed it on with serger, then I added a straight line on the regular sewing machine so that the edge doesn't turn. You just should stretch the fabric a little if you want it to stay elastic.
Before.
After.