This wool is more like aran than dk and the mitts were too large as written, even using a smaller hook. (Also the fabric was too dense.)

So, with a larger hook than suggested in the pattern I made a wrist band of 15hdc blo, then a row of sc blo, then joined using surface crochet. (Video for join is here.)

I put 2 sc into each row end of hdc, giving 32 stitches, then proceeded as the pattern.

I did 6 rows (3 lots of shells) before the thumb join. The shells part is much wider than the rib and effectively formed a gusset for the thumb.

I made the thumb space by doing 4fsc across a gap of two shells. This gives a thumb of three shells, and a hand of 6 shells. I did this at the end of the round on one glove and the beginning of the round on the other so that the join is in the palm of the hand. This meant continuing with the thumb before starting the palm on one glove.

At the top of each mitt and at the top of each thumb I used shells made of three stitches instead of four to reduce any bagginess.

The half-finished gloves show how far I got with one ball of the Drops Lima yarn.