Chainmail coifs were a thing, but they typically also covered the shoulders. Normally there would also be some padding underneath.
Sometimes a helmet would be worn over the coif, so your helmet with a coif is historically plausible.
The horns are a fantasy invention. In reality, soldiers would not wear a helmet with horns because they can catch weapons (which you really want deflected off), and because they can be grabbed. Both cases allow the opponent to yank the wearer's head around, which is obviously a bad thing. However, this is fantasy, so a horned helmet is fine.