If you want to have a go reading manga etc,
Jコミ is a legitimate online source (re-prints of older, now out of print manga, there are a few ads but I don't find them obtrusive). The bonus here is that you don't have to pay your own money to find out that you're not at that point yet. They have a few 4コマ collections and some light novels as well. Some of the stuff labelled 少女 or 少年 may be kanji-light or furigana heavy (it varies: I just looked at two and found one in the generic fantasy genre called 精霊ルビス伝説 which has furigana on just about all the kanji, and another sports manga which had pretty much none). N3 is not a good guide to what you know about casual grammar so it's kind of hard to judge how you'll get on.
I've probably linked to this about 100 times but I'll do it again:
ESL Reading Lesson - Using Context for Reading Literacy
And also, there's no point forcing yourself to read something that you're not interested in. If it actually turns out to be too hard for you, and it's frustrating, or if it actually turns out to be a bit crap and doesn't hold your interest, you can just stop reading it.
One of my favourite books from when I was very young starts: Each peach, pear, plum, I spy Tom Thumb. It's a great book for kids, full of rhymes and references to fairytale characters, with good illustrations. I would happily buy it as a gift for a young child. It would be
terrible for someone who was learning English - it's full of references to obscure fairy tales they probably don't know and bits of doggerel that don't even mean anything.
I actually think non-fiction is an easier starting place, e.g. stuff for twelve year olds in the form of recipes, home experiments, how to build (X), manga explanations of complex things (I once saw a manga explanation of the British elections in a Japanese newspaper, it was hilarious).