crocheting mittens

[fatoldladyinpjs]

Okay, I'm a beginning crocheter. Just finished my first pair of mittens. One thumb a bit bigger than the other, but fixable. My question is about the holes for single crocheting. Maybe I'm not getting this. The single crochet in mittens comes out more like a mesh and isn't solid. Are these mittens all that warm, especially in northern climates like mine? Granted, I did use a larger hook J for practice. Do these holes get better with smaller size hooks? What hooks would you recommend? Am I supposed to use a smaller hook to do the cuff? Is there another stitch other than single crochet that would make these mittens less holey?