Are they on Natively? Anything between L14 and L22 with furigana is usually a good fit difficulty-wise. (Apart from that, the ABBC mostly reads manga. Short stories and children’s books have a very hard time getting votes. And I don’t think graded readers fit well since people can just read those on their own.)
You can also just post a link to something in the ABBC thread asking if that looks good for the club if you want a second opinion before properly making a nomination post.