Those 18 posts got you out of Google's newbie sandbox and that's a good thing. It means you have a solid chance at ranking for money-making posts if you're consistently making an effort with content and SEO.
Be clever with where you link to the affiliate posts- because if the informational pieces are bringing in 80% of your traffic, you're gonna have to do your absolute best to drive them to the money posts (WITHOUT being intrusive)
See if there's any room for improvement in your affiliate posts. Both in terms of copy and SEO.
Affiliate posts need copy, not content. You're trying to induce NEED in the reader, to do that you reaaally need to know what you're talking about. Stuffing keywords and adding endless H2s for the sake of it will get you traffic, but barely any conversions.
It's so important to be more than just another "best-catpoopcooper-reviews.com" site in the Google sea. Take the time to stalk the kind of people who read your stuff. Yep, I said stalk. If your speak their lingo and know their frustrations, selling to them will get way easier.
Write copy that induces instant connection and trust in the reader- they'll know you mean well AND they'll buy through you.
If you're just outsourcing the writing part of it and not the keyword & competitor research stuff, I'd say you're better off sending them bulk work.
Throw in a month's worth of blog topics (and the keywords for it) in an excel sheet, add a "Publishing Date" and brief instructions with affiliate links they're supposed to use.
Ask your writer to mark the topic "Done" when it's drafted in the CMS and have them drop you a text whenever a post is ready to go live. If you don't have an editor, head over to the draft, edit, add pictures and viola! you're done.
You'll avoid the constant back and forth of sending one topic at a time this way.
P.s. I write optimized affiliate blogs and web copy for blog owners like you. Let me know if you could use another hand on this site :)