I carried an M9 in a Galco Concealable OWB, but in uniform, so I had a loose ACU top to cover it. It's a quality, pretty comfortable holster that conceals well - it really hugs your side and blends in because of the smooth leather construction. However, because of how long the M9 is, the bottom tip of the holster pressed into my right "cheek" and started to give me sciatic nerve pain if I wore it for too long. I reached out to a friend who carried an M9 IWB in civilian clothes. He had a good looking design that featured a large leather panel that spread the bulge out well when he wore it at almost 5 o'clock.
I was fortunate that I carried a Glock 19 on one deployment in civilian clothes, so smaller pistol with lots of options. I used a Milt Sparks Versa Max 2, which you could order for the M9, but it's an expensive (and long lead time) holster to "test" if it doesn't work out for you.