I don't think much of belly sweats myself, but believe that almost any mini neck can be improved with a neck sweat. I use a throatlatch sweat first (2" or 3" wide) and then put a neck WRAP over that - usually one of the narrower ones (6" I think). I use the kind that can be left on overnight and also use them when the minis are worked. As long as they are taken off for a while every day, and their turnout buddies don't try to remove them, they can be left on most of the time.
There is a knack to putting them on so that they are tight enough to work but not too tight. I think most people (I know I did) put them on too loose at first. Pull them tight, just make sure you can get a couple fingers under them. Also, they loosen when the horse puts its head down.