I have finished both mitts! I undid the cast-off of the first mitt’s hand and redid it much more loosely so they fit me a lot better now.
It turns out that the more I wear these mitts the looser they become. This yarn seems to do that because the socks I have made with it are the same. This means that these mitts are perfectly sized after a couple of wearings!
I am going to knit the second mitt for completeness’ sake.
Have finished one mitt but they are very tight on my big hands and so I am not sure about knitting the second.
I am using magic-loop rather than DPNs because I do not have DPNs in these sizes.
I cast on with a tubular in-the-round cast-on (youtube) on 2.5 mm needles and did not start knitting tbl until the next row of ribbing (on 2.25 needles), i.e. row 2 of the ribbing.