Digital Dudz shirts use industry standard t-shirt sizing so pick the size you normally prefer for a t-shirt and you should be safe. If you are on the borderline between sizes, it is better to go with the larger size as you will have the pocket and mobile device to accommodate in the front (but this generally doesn't make much of a difference).
iWounds are all "one-size-fits-all"
T-Shirts (100% heavy cotton)
Morphsuits Size Guide MorphCostumeCo Size Guide