So far I've cast on the same 68 body stitches for every size from Sia through Hound, and it's worked just fine. The ribbing is stretchy enough that it conforms to whatever doll I'm knitting for (though I haven't tried it on Yukinojo yet; I'll report back when I do). Sizing only varies in the body length, sleeve length, number of sleeve increases, and turtleneck length--things that are easy to check and adjust as you go.
Ribbed turtleneck for Hound et al:
Sportweight yarn (I used Lion Brand Wool-Ease sportweight)
US size 3 (3¼ mm) double-pointed needles
US size 3 circular needle, 11”
US size 5 or larger needle for casting on; US size 9 or 10 needle for binding off neck
4 stitch holders
Body: Cast on 68 stitches. Divide on size 3 DP needles and join, being careful not to twist. Work in K2P2 ribbing for 4” (waist-length sweater) or 4½” (hip-length). Leave this piece on a length of scrap yarn while you knit the sleeves.
Sleeves: Cast on 24 stitches. Divide on size 3 DP needles and join, being careful not to twist. Work in K2P2 ribbing for 2”. Mark a pair of stitches (two K stitches or two P stitches) with a safety pin or stitch marker; beginning at about 2”, increase one stitch on each side of these marked stitches every 8 (or 10; this isn’t a big deal unless you’re obsessive) rounds until you have 36 stitches total. Keep knitting on these 36 stitches in K2P2 ribbing until the sleeve is 8½” long, or 9½” if you want to turn back the cuffs. Leave the first sleeve on a length of scrap yarn while you knit the second one.
Now for the fun part! From here on out, I’m pretty much quoting directly from Elizabeth Zimmermann’s book Knitting Without Tears, pages 69 and 73-75. It’s worth tracking down a copy if you don’t have one; with this book, you can figure out a lot of different kinds of sweaters for any size doll or person.
You are about to unite body and sleeves on one needle. Some stitches will be left on holders at the underarms of body and sleeves. The remaining stitches of body and sleeves will be combined to form the raglan yoke.
Put 8 stitches on holders at either side of the body, so that there are the same number of stitches on what will become the front and back of your sweater. The stitches on holders are the underarms. Be sure to have the underarm holders of the body-piece exactly opposite each other. On each sleeve, put on holders the 8 stitches that are directly above the line of increases.
When the four blocks of 8 stitches are all on holders, unite all the remaining body and sleeve stitches on the 11” circular needle, matching the underarms. Before you start knitting again, make sure that your K2P2 ribbing continues unbroken all the way around. Rejoin your yarn at any convenient place, such as the middle of the sweater back (stay away from the sleeves, at least the first time you try this pattern), and mark your beginning stitch. Knit 4 rounds in K2P2.
Put a safety pin or stitch marker at each of the four places where the body and the sleeves join, marking either a pair of K stitches or a pair of P stitches. Make sure that you have exactly the same number of stitches for each sleeve, and exactly the same number of stitches for front and back. You will decrease 2 stitches at each of the four marked places, every other round, like this:
*Work to within 2 stitches of the first marker. Decrease (either K2 together or P2 together, depending on which kind of stitches you’re confronted with). Work the two marked stitches. Make the opposite-slanting decrease (SSK or SSP).* Repeat from * to * three more times. This completes your first decrease round; you have decreased 8 stitches total. Work one round in pattern, knitting the K stitches and purling the P stitches.
Continue knitting, alternating the decrease rounds and the plain pattern rounds. You will soon find that it’s easier to switch from the circular needle back to the DPs. Keep decreasing in this way until you have 44 stitches left. Work around on these 44 stitches in your established K2P2 pattern for 2½”-2¾”. Bind off very loosely, using a large needle (size 9 or 10).
Almost done! Now you need to close up the gaps at the underarms. Do this by grafting or very loose 3-needle bind-off. Turn the sweater inside out, weave in the loose ends of yarn, close up the little holes at each corner of the underarms, and weave in those ends. Turn sweater right side out. Put on your Hound. Admire.