I took a little time over the weekend to swatch. I used size 10.5 (i.e. 6.5 mm) needles. I used two strands of yarn together at the same time.
At first, I tried 1x1 ribbing over 20 stitches with a 3x3 Lily Chin ribble in the center. Not bad, but the knit stitches of the ribbing just don't do anything for me. I like cables set against a wavy reverse stockinette stitch background. The problem for me with the ribble technique is that you can't get the purl background. Changing to purl 1, knit 1 for the background doesn't make the purls jump forward and the knits recede backward. You can see on the swatch that I tried it, just to be quite certain. (And as I write this, I'm suddenly wondering if doing the background in garter stitch would have worked.)
I do, however, like the thickness and double-sided quality of the ribbles. Especially in this fuzzy yarn, cables need to be big and burly to show. Stitch definition in this fuzzy alpaca? -- see Myopia or Astigmatism.
The Lucy Neatby double knitting class was also fresh in my mind. She started us out with knit 1, slip 1 with yarn in front. This is a technique I've tried before, but had quickly dismissed and not explored. Partly I hadn't explored it because I typically double-knit for color patterns, in which case I'm using two different yarns. But here where it's all the same yarn knit 1, slip 1 wyif (or purl 1 slip 1) is good. So, I quit knit 1 purl 1 ribbing and tried double-knitting using the work 1, slip 1 technique. In this case over 20 stitches, (purl 1, slip 1)2x; (knit 1, slip 1 with yarn in front)6x; (purl 1, slip 1)2x. This established reversible reverse stockinette stitch at the selvages with a nice line of double-knit up the center.
My first attempt at a cable involved the fiddly business of separating the front and back layers, working the cables independently, and then re-integrating the stitches. Very time-consuming, but it does produce a cable on both sides of the fabric. The cable did seem to lie a little flat to me -- not quite as thick and burly as a ribble. You can see this at right, on the bottom cable.
My second attempt was a modified ribble, the middle cable at right. I figured, if cabling across ribbing works, why not cable across double-knitting? The cabled section has 12 stitches -- six obverse stitches and six reverse stitches. I put six (3 obverse & 3 reverse) on a cable needle and held those in front. Then I worked the next six as (knit 1, slip 1 wyif)3x. Then I worked the cabled stitches as (knit 1, slip 1 wyif)3x. Then I finished working the purl background. When I came back across on the wrong side of the work, it was a normal work 1, slip 1 row. The result is quite good -- thick and burly like a ribble, and easily incorporated into the slip-stitch double-knitting method.
My third attempt was a ribble for true comparison. This is the top cable in the picture at right. The problem here is that slip-stitched double-knit takes a full circuit to complete one row. Work across, turn, work back across, turn. Each side of the fabric now has one more row than it did at the start. A true ribble works all the stitches, both front and back, on the same pass. So, I was going to end up with stitches in the center cable that were worked and stitches in the purl background that weren't. The solution: (purl 1, slip 1)2x, turn. Repeat this twice more. So now you are at the right edge of the cable/ribble. The first group of background stitches has been worked 1.5 times.
Work the 3x3 ribble -- knit 1, purl 1 over 12 cabled stitches. Ribble completed.
Work the background stitches on the other edge: (purl 1, slip 1)2x, turn. Repeat this 3 more times. Thus, two full rows of knitting have been added to that group of background purls.
Now, work across the ribble in knit 1, purl 1. Two full rows of knitting have been added to the cable/ribble section.
Finally, work (purl 1, slip 1)2x to finish the last half-row of background purls at the other selvege.
Can you see why a true ribble is not a great idea here? Circles within circles.
Addendum: I went and checked if the ribble would work with garter stitch as the background. It does, but I'm not as happy with it as the slip-stitch double-knit. Even using two strands together, this yarn is too thin as a single layer fabric to be a blanket. Double-layered it is thick enough to be substantial. And it just feels like something thick and fluffy and perfect for hibernation.