2 old t-shirts, a pair of scissors, a sewing machine, and you could do this in a flash. A good use for those shirts that used to fit. I think I'd use a black or navy blue shirt for the back (any dark color) and something flashy for the front. Have the back wrap slightly to the front and it would be very slimming.
Oversize Raglan Shirt Long Sleeve - Womens Clothing Black Top Small Medium Large. $44.00, via Etsy.