I'd say that COH fit true to size BUT they don't stretch as much as 7FAM, R&R, Jbrands. So i'd defintely recommend trying them on before purchasing them just because you might have to size up due to the denim not completely stretching out.
COH runs TTS. As to how much it stretches depends on the wash. Most of the washes that have come out as of late are all lightweight denim and they stretch out far more than the heavier weight denim that they used to use all the time.