This is super off topic but I’ve only recently heard of this series and until I saw this post I thought it was another name for The Magic Faraway Tree by Enid Blyton FML.
BTW OP when you go to bookoff I also recommend looking at the childrens literature section in general. I think theres a wide range of interesting books there, and I find kids novels easier to read than manga, personally!
The book i would recommend you the most would be this Japanese folktales book for japanese learners.
It contains 23 short common japanese stories with integrated vocab list after the story to look up, and it also cleverly stops showing you furigana after 2-3 usages of the same word. The order of the stories and lengh is based on difficulty, so you can progress with the book. This book is completly independent, you don’t need a dictionary trqanslator which really is refreshing after your ordinary manga grind.
Also, since people mention bookoff, use this bookoff website if you know the titles of manga you want to purchase. Often times a single bookoff store will not have items you are looking for, so browsing in their inventory and getting it delivered to a certain store is key.
Read anything that’s fun to you.
I can’t really talk about manga since I almost immediately went to novels and light novels.
When it comes to novels, starting out is extremely hard no matter how you approach it. And even “easy” novels use high level grammar here and there. Do whatever you can to make it easier for you. Read novels of which you already know the story through anime or manga, or maybe even through being familiar with a translation. That way, when you get lost you can find your bearings again. Also reading digital is probably the way to go for the first couple of years. You can read physically if the book has furigana, looking up words without furigana it is just not worth the effort when reading physical books. I buy the physical books and then download then yarrr the digital version for koreader.
if you for instance, like Frieren, there is a novelization with furigana. The novelization is based on the anime (which is in turn based on the manga) and covers season 1.
時をかける少女 is a short classic story. It’s quite easy, but it does get very sci-fi-y in the end with lotsa sci-fi words. The book is only 160 pages but that includes two short stories as well.
You can also find more books on LearnNatively, there you can filter for difficulty based on ratings of other Japanese learner users.
Also, I also live in a “Japanese desert”, but I still managed to get a decent collection of Japanese physical books through amazon.jp. They ship to me in the Netherlands, so I assume they ship to the USA as well. And you can view the website in English. Just order in bulk to minimize shipping costs. It’s still not cheap by any means, but the low Yen value makes it affordable, and unlike some websites you CAN pay with foreign credit cards. Of course, buying books while visiting Japan is still a lot better, but don’t feel too discouraged if you can’t find (or carry) everything you’re looking for there!