Loads of different makes have belly covers with the rugs. If you mwant 'maximum' cover then a Boett rug will do that better than any, but that comes at a premium price.
I use the rambo sweet itch hoody its brilliant , , horse hasnt got sweet itch but he does get bitten to bits and they really do protect him, premier equine do one as well, go my oldie in one of them, they are very similarand just as good
If its sweet itch then go for the DeMeulenkamp "Itch-Off" rug its similar to the boet but i found it better for the pony ive got with sweet itch and its cheaper, dont go for the pogony qualitly and sizing not as good.