Get whatever one you can get your hands in and out of easily. I have huge hands. Combine that with a release for my bow, and most muffs suck. I hate the muff on my iwom, and actually have to take part of it out. My hands don't fit in there, and if I do get them in, its quite painful when you lose all the blood flow to your hand.
Best muff I have is an old cabelas thinsulate muff. Honestly I think it was like $10. Super cheap. But its thin, light, and has the biggest hand openings ever. All you should need is to block the wind from your hands and they will be plenty warm. Last thing you want is your hands to sweat.
Should be able to just put it around your upper waist and adjust the slack whether you want your arms/hands above or below your bridge. Won't fall off since your saddle will hold it up, and won't get in your way anymore than anything else you have on since it will be contained by your set up.