Modifying practically everything about this pattern.

Left Mitt

CO the larger stitch count. Work in 1x1 twisted rib for 2½“.

2 rnds with MC.
5 rnds of Detail Colorwork Chart modified to be divisible by 8 using AC1, AC2 and AC3.
2 rnds with MC.

Start thumb gusset:
K to 4 sts before end of side, pm, M1R, K1, M1L, pm, K to end. K 2 rnds even.

Increase for thumb gusset 2 sts every 3 rnds until there are 17 sts between markers.

K to marker, rm, place next 17 sts on holder for thumb, rm, K to end. K 1 rnd even.

15 rnds of Main Chart modified to be symmetrical in both directions.
1 rnd with MC, catching the floats.
2 rnds with MC.
5 rnds of 1x1 twisted rib.
BO.

Thumb:
Pick up 17 sts + 3 sts from the gap above thumb. K to last 5 sts, SSK, K1, K2tog.
6 rnds with MC.
5 rnds of 1x1 twisted rib.
BO.

Right Mitt

Reverse thumb gusset shaping:
K across back sts, K3, pm, M1R, K1, M1L, pm, K to end.

MC: Auri (25 + 43) - 38 = 30 g
AC1: Sake 33 - 23 = 10 g
AC2: Haave 47 - 41 = 6 g
AC3: Valo 21 - 17 = 4 g
AC4: Rae 23 - 22 = 1 g