This went through a few iterations; here’s what I ended up with:

second: ribbing on 5.5 mm; rest on 7 mm
CO 30.
10 rounds 1x1 ribbing.
switch to larger needles.
Dec 2 on first round.
Knit 3 rounds plain.
Round 1: k1, pm, k1, pm, k to end.
Round 2: k1, sm, M1, k1, M1, sm, k to end.
Round 3, 5: k
Round 4: k1, sm, M1, K3, M1, sm, k to end.
Round 6: k1, sm, M1, K5, M1, sm, k to end.
Round 7: k1, put thumb sts on holder, CO1, k to end.
15 rnds st st. On last rnd, knit next 2 sts from next rnd; this is new start of rnd.
k1, ssk, k8, k2tog, k1
k
k1, ssk, k6, k2tog, k1
k
k1, ssk, k4, k2tog, k1
k1, ssk, k2, k2tog, k1
k1, ssk, k2tog, k1
kitchener last 8 sts

For thumb, pick up 2 sts in gap, then knit 8 rnds.
Next rnd: k2tog, k1; rep 2x.
Next: k2tog; rep 2x.
Cut yarn and thread through sts to close.