Best we have is eastern orthodoxy. There are records dating back quite some time.
Changes likely have happened, especially when language changes, but the records are strong and tradition is tradition.
If you haven't, I suggest you attend Orthodox Saturday night Vespers followed by Sunday martins and Divine litergy.
See what it feels like and talk to the people after services. Ask questions.
And by nature of protestantism, you can't really expect continuity, though I'd bet Lutherans are the closest.