Despite all the low expectations of Facebook, I'd go ahead and get a page, which means you'll need a profile, too. (The two are separate entities.) It's free, so that takes some of the pressure off.
A Facebook page is just...expected. It's still the most popular form of social media, so that means that when you get some readers, some of them will prefer to find your updates there. Definitely manage your expectations, but also regularly post something related to your books. I've got a scheduler, so I have one or two posts automatically every day--things like quotes from famous fantasy authors, funny memes, pretty internet pics of scenery. All my blog posts automatically post on Facebook as well, and everything that posts on Facebook automatically tweets (make sure you don't do that in the other direction--a dozen tweets in a day are no big deal, but that's kind of overwhelming on a Facebook feed).
It doesn't net me a whole lot, and I don't pay for boosted posts. I think of it mostly as a courtesy to anyone who prefers to get info that way. My advice would be to brand it correctly, set up regular posts to it, and then simply check it every few days or so. It hasn't been worth spending a whole lot of time on, but I wouldn't completely do without it, either.