Not sure if you need a copy editor? Read what other writers have to say about the matter:

"As she read through the manuscript, INTERN started to feel more and more mortified. The copy editor had caught so many silly mistakes, pointed out places where a topic mentioned in an introduction was never addressed in the chapter, and even raised questions about the political correctness of some of INTERN's word choices. 'Oh man!' thought INTERN. 'Copy Editor must think INTERN is a fool! Copy Editor must be wondering what Publisher was thinking when they offered to publish such a cretinous and unworthy INTERN!'" - THE INTERN

Read the whole article: Hail to the Copy Editor

"For those who don't know what a copy editor is let me just say this: A good copy editor is to a piece of writing what the Secret Service is to the President: protection of the most profound type. She (and most are women) stands between excellent writing and disaster. She is the one who asks if you really meant to say that direct medical costs for asthma in the United States are $11 million a year, or $11 billion a year (the latter). She is the one who realizes you skipped a reference and now none of your endnotes are in the right place. She is the one who knows that you really mean to write multiple sclerosis, not muscular dystrophy.

"Bottom line, she is the one who can see the trees in the forest when the writer can barely even see the forest anymore." - Debra Gordon

Read the whole article: Ode to a Copy Editor

"Maybe most apprentice writers don’t think that copyediting and proofreading manuscripts are issues of craft, but if they don’t, they’re wrong. These are the most basic craft matters in the book, in any book. Professional writing must be 100% clean. It must be free of errors in punctuation, usage, mechanics, and spelling. No typos. Period." - Diana Hume George

Read the whole article: Copy Editing. Vital.