You can take a knit sweat top or knit mock turtleneck (Target has them) in your size, and fits well on your jumpsuit, and cut the sleeves off from the armpit to about 3-4 inches off the shoulder. Then take to one of the tailors (there is a Chinese lady I took mine to, she was great) and describe how you want detail added, like the vertical stitching that goes down the flap sleeve and the double hem.
If your mom or girlfriend sews, it is cheaper. I paid around $125 for a Jango vest made without a pattern. Or you could just go with the trimmed knit shirts. Since your suit is custom, scrutiny most likely will be less.
Good luck my man!