/cgl/ - Cosplay & EGL

Can someone give me a hand? I'm about to tear my hair out over this.
I'm using Photoshop so I can convert this to CMYK (I didn't work in CMYK from the start because I work in SAI, my pressure sensitivity doesn't work in PS and the program is hell on my CPU).
The left image is when I have my Proof Setup set to Working CMYK so I can preview it or whatever. The right image is after I actually convert it to CMYK. A ton of detail is lost and the black isn't black enough. I know that the reason for the loss of detail and ugly grey edges is because CMYK doesn't have enough of a color range to properly represent those subtle shifts in color between the purple and the black, but I have NO idea how to get around this problem. It looks like this no matter what colors I choose because CMYK fuckin suuucks and I'm an idiot.
Does anyone know how I can retain the detail in CMYK? I've spent hours trying to figure this out. My last resort is to just go full black & white, but B/W prints don't sell as well as colored prints.