I imagine you’re getting to a point where you’ll be fine reading some manga without furigana, but if you’d like to try something a bit transitionary (furigana on some kanji, and not on others), we’ll be reading 耳をすませば in the Beginner Book Club (starting next month) which is just that!
As others have mentioned, putting in a Japanese address is necessary. It should work out on your Kobo account, but if you plan on using that for anything non-Japanese, I recommend creating a new account for Japanese-only use (should you decide to give Kobo another try).
I expect this one to be very difficult, but that just means it would be very rewarding if you stick with it and learn along the way. (This is one of those series that isn’t available digitally.)
This is where it’s great if there’s anything of interest that we’ve read in a book club, because there are discussion threads with discussion on grammar, vocabulary lists, and you can ask questions even years after the book club ended and often get a response in a decent timeframe. It makes it a lot easier to gain knowledge and expand your reading capabilities.