You only need to cover your shoulders where they specifically ask you to. Many orthodox churches in eg Greece, I think St Peter's Rome.
Don't worry about it. If you'll be warm enough with shoulders uncovered, then fine.
Def no fascinator - not with that glorious hair - though you could put a flower or something in the knot. I wouldn't, more expense, faff, it's lovely as it is.
Have a great time.