I didn't even think about that with fleece. I'd probably have to add quite a bit for the seam allowance and what my son calls "the squishy factor". It's the amount of room inside a garment/quilt you need to squish around in. I love the name he gives stuff.
I wonder if I made mittens if he'd be willing to wear the cheapy gloves under them. He can't tolerate it when his skin is cold, so it's difficult for him to wear mittens. I bet my other ones would though!
Thanks again!