Using the larger circular needle cast on 12(12)16(16) sts and purl the WS row. Work stockinette st flat. On every row increase 1 st at both ends inside the edge sts (= yarn over; on the next row knit or purl it through the back loop). Repeat the increases 17(19)19(21) times in total = 46(50)54(58) sts. Leave the sts on hold.
Using the larger circular needle pick up 12(12)16(16) sts from the cast-on edge and purl the WS row. Work stockinette st flat until the front crotch measures 3(3,5)3,5(4) cm. At the end of row at both ends cast on 2x2 sts, 1x3 sts, 1x4(5)5(6) sts and 1x6(7)7(8) sts = 46(50)54(58) sts.
RS: work the 46(50)54(58) front sts, place side marker, work the 46(50)54(58) back sts, place marker (= beginning of round). 92(100)108(116) sts now on the needles. Work stockinette st in the round.
When the body measures 2(3)3,5(4,5) cm, decrease 1 st on both sides of both markers: *k1, skp, work stockinette st to last 3 sts before marker, k2tog, k1*, repeat *–* once more. 4 sts decreased. Repeat the decreases every 2(2)2,5(2,5) cm 3 more times = 76(84)92(100) sts.
When the body measures 10(11,5)13(14,5) cm, work more height to the back piece with short rows: work 38(42)46(50) front sts, slip first marker, work to last 4 sts before second marker. Turn work. Slip 1 purlwise with yarn in front, tighten the yarn in the back of the work so the loops of the slipped st from the previous row come over the needle = double stitch. Purl to last 4 sts before next marker, turn work, double stitch. Keep working short rows, turning the work 4 sts before the previous double stitch. Work until there are 3 double stitches at both ends.
Next round: knit to end, knitting the legs of the double stitches together as a single stitch. Knit 1 round, knitting together the remaining double stitches.
Opening for string: k19(21)23(25), turn work. Purl to previous turn, slipping both markers. Turn work. Work 3 rows in stockinette st, then knit the WS row (= fold row). Next round: knit to beginning of round marker. Work stockinette st in the round for 4 rounds. Bind off loosely. Fold the opening and sew it to the WS.
Using the smaller circular needle pick up sts from the top edge of the opening. Start at the left end (former beginning of round) and pick up 1 st per each purl st on the fold = 76(84)92(100) sts. Place marker for beginning of round. Work ribbing in the round for 2 cm.
Switch to the larger needles and work as follows: work 3 sts in garter st, k5(7)6(8), place marker, k22(22)28(28), place marker, k5(7)6(8), work 3 sts in garter st and bind off next 38(42)46(50) sts (back) loosely. 38(42)46(50) front sts remaining.
Begin the lace pattern on row 1 of chart I(I)II(II): work 3 sts in garter st, k5(7)6(8), slip marker, work the lace pattern, slip marker, k5(7)6(8), work 3 sts in garter st. 1 st decreased, 37(41)45(49) sts on the needles.
Row 2: (WS) work 3 sts in garter st, purl to marker, work next row of chart I(I)II(II), purl to last 3 sts, work 3 sts in garter st.
Row 3: (RS) work 2 sts in garter st, skp (= slip 1 knitwise, k1, pass slipped st over), knit to marker, work next row of chart, knit to last 4 sts, k2tog, work 2 sts in garter st. 2 sts decreased.
Repeat rows 2–3 4(5)5(6) more times = 27(29)33(35) sts. Work even until you have worked row 22.
Work garter st for 8 rows with all sts. Next row: k7, leave the 7 sts on hold, bind off next 13(15)19(21) sts, work to end.
With the 7 sts at the left end work garter st for 16(17)18(19) cm or until the strap is 2 cm from desired length. On the next row make a buttonhole: k3, yarn over, k2tog, k2. Work garter st for 2 cm, then bind off. Knit the other shoulder strap in the same manner.
Cuffs: using the 3½ mm double-pointed needles pick up 46(48)50(52) sts from the leg opening and divide them onto four needles. Work ribbing in the round for 3 cm, then bind off in pattern.
Work the other cuff in the same manner.
Sew the buttons onto the back piece, at the edge of the ribbing. Steam and shape.
I-cord string: k4, *do not turn work. Slide the sts back to the right end of the needle. Hold yarn in back and k4.* Repeat *–* until the string measures approx. 90(100) cm. Break the yarn and pull it through the sts. Weave in the ends.
Pass the string through the opening and tie a bow in front.