Improvised pattern:
CO 56 st. Knit 2, purl 2 for 7 cms/26 rounds. Continue in stockinette st for 28 st, then purl 4, knit 4 the remaining of the round. Repeat for 5 rounds total, then purl over the knitted st and vice versa for 5 rounds (but continue with stockinette for 28 st = the back side of the mitten). Continue with this pattern for the entire front side of the mitten.

After 10 rounds, start increases for the thumb: knit 4, inc 1, knit 3, inc 1. Increase every 4 rounds (outside the previous increases) until you have 15 st for the thumb. Place these st on a piece of scrap yarn. Pick up 3 new st behind the thumb on the next round.

24 Nov 2020: Picking up again this hibernated project! :)