Quick apostrophe help please.

[Pipbin]

I just want to draw on the wisdom on the MN crowd to see which is correct or preferred.

Should it be James' coat or James's coat?

I know it is a tricky one and what is correct seems to depend on the day of the week.

James is not a real name right? James. James. I've read it too many times.

I always follow the rule that if a singular noun ends in an 'iz' sound, you don't use the extra 's' because when said out loud it's awkward (think Moses's - spoken Moziziz, sounds dumb).

James doesn't end in an iz sound so takes the extra 's'

Disclaimer: was last a copy editor about 20 years ago so fashions may have changed.