The HH #4's work just fine for my BMJ ... but you could probably use #3's too for an even more slender fit. Would definitely not go #2 as tighter fit isn't necessarily a good thing when pulling skins on/off.
I also respectfully disagree with those who forgo the skins for a stuff sack. For me they're like backpack hipbelt pockets, you don't NEED them, but they sure do come in handy. Even on a sunny day I'll string the tarp up knowing I can deploy it in seconds if needed. While skinned, the tarp is completely out of the way and I can still see the stars at night. Makes it easier to pack up too. Honestly, it's one of my favorite "accessories". To each their own I guess.