Use one strand alpaca with one strand silk. The silk is VERY thin. As thin or thinner than sewing thread.

My gauge was less stitches than required gauge, after wash/block.
Pattern 24 st = 4” (5.05 st/inch)
My Gauge 24 st = 5.5” (4.36 st/inch)
Since I liked the look of my gauge swatch, I did some math and instead of changing my needles to match gauge, I changed the size I made. Normally, would make an XL if gauge met. Made size medium instead to equal stitches per inch to match bust measurements. Fits perfectly! The math is a PIA, but so much better that swatching and reswatching.