Convert CMYK Brushes to Duotone

I have two high-resolution Photoshop files of cosmetic brush illustrations currently set up in CMYK. I need each image converted to a true duotone that will print flawlessly with just black plus one spot PMS ink. The finished art must keep every subtle highlight, mid-tone, and shadow so the brushes still look as refined as they do now—simply stripped down to two inks for screen printing.

I haven’t picked the exact PMS color yet, so please suggest a hue that complements cosmetics packaging while offering good contrast alongside solid black. Once we agree on the swatch, apply it consistently to both files.

You’ll receive a single 17 MB zip containing the layered PSDs. Feel free to work in Photoshop Duotone mode, Gradient Maps, or any technique that preserves detail and smooth tonal transitions. When you’re done, send back print-ready files I can drop straight into an Illustrator layout—PSD, TIFF, or another linked format is fine as long as spot colors remain intact and separations read correctly.

Deliverables (both images):
• Final duotone files with embedded PMS + Black channels
• Preview PDFs showing the spot plates

Let me know your proposed PMS choice and expected turnaround, and I’ll forward the download link right away.