A Grammar Problem

While it is more grammatically correct to add an 's to Lucas's name to show possession, The AP style guide recommends only to add an apostrophe, as in Lucas'. The Chicago Manual says to add the 's if the name doesn't end in a z sound. Most will say either is interchangeable and acceptable. I lean toward being more grammatically correct, but would hate people to think I am oblivious to grammar conventions. I didn't consider this would be such a problem until I sent an invitation for my son's baptism. My husband thinks it's wrong to add an additional 's. When you pronounce the name of someone whose name ends in s in the possessive form, don't you pronounce the extra s? This is why I don't mind it. S' always looks like a plural to me. I get obsessed about the most meaningless things. See below sling post.