I don't ride english but I can tell you a break-away halter is just a regular halter with leather or velcro that will "break away" if it is caught on something. Its a safety halter used for turnout. Oh, and I'm sure you will need a saddle pad and possibly some reins. Not all bridles/headstalls come with them.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France