I knit tons of mittens for my adult kids and for charity. You'd need about 100 grams if you're doing it in wool. I used Cascade 100% Peruvian wool. Not sure of the yardage in those. I used one Cascade skein and two Knitpicks Wool of the Andes 100% Peruvian wool skeins. The two yarns are similar, but I think the WOA would be more like a light worsted. My son has a pair made with those that he loves. And the ones I did for him were convertible mittens that used more yarn. I used two WOA skeins. Keep in mind that the Cascade is 100 grams and the WOA is 50 grams. The Knitpicks seems like more of a bargain, but the skeins are smaller. However, even if you have to buy two, I find it's still cheaper to order from them with the shipping and save money over name brands and LYS prices. My LYS raised their prices 33% so I don't shop there anymore.
Edit: I should add that I knit my mittens and gloves with a #7 or #8 needle. Everybody's gauge is different. Mine runs about about 4 1/2 stitches per inch on the 7 and 4 stitches per inch on the 8, if that helps. Yes, I know. I'm sloppy when it comes to gauge but it works for me. Have done these mittens so many times I know the exact cast on number, measurements, and could do them in my sleep.