When I buy a shirt that is too short, I watch for the same shirt to go on clearance, and buy it in another color. Then I cut the bottom four to six inches off and using the original hem line on the upper shirt as a guide, sew them together. I also do the same to the usually too short sleeves, but I have bought a mans T-shirt at goodwill and done the same thing. The best advice I can give you is use lots and lots of pins.