The most common names for beginner textbooks are Genki and Minna no Nihongo. Genki looks pretty good from what I’ve seen, but I haven’t used either series. (Genki has translations for the dialogues in the textbook, and comprehension questions are posed in English, at least initially, so it’s beginner-friendly.) I learnt my Japanese basics from a French publisher called Assimil. Their French edition claims to bring you up to a B2 (roughly mid N3-low N2 level based on my experience), while their English edition is currently only able to bring you up to A2 (about N4 standard, I think?). I think their approach to language learning is really good though, and Assimil’s target audience has always been self-learners, so you might want to check it out, even if it’s just for the English edition. (They should have samples available somewhere…) Both editions are meant for beginners, by the way, it’s just a matter of the amount of content available.
For intermediate textbooks, I’d recommend Tobira (roughly N3-N2 level) because it focuses on introducing various aspects of Japanese life and culture, so you get to learn about Japan and pick up genuinely useful words (instead of pretending, for instance, that you’re a foreign student living in Japan and following somebody’s scripted life). I feel that the texts and dialogues are pretty authentic – the articles at the very least remind me of NHK articles, except that they’re usually a little easier and come with vocabulary lists. Speaking of Tobira, they have a beginner’s textbook coming out in 2021. (It’s just FYI, but I’m pretty sure you’ll be more than advanced enough for an intermediate textbook by then.)
For advanced textbooks (i.e. for getting to high N2-N1)… I have a recommendation from a fluent friend, but it’s sitting on my bookshelf at home and I can’t remember the title. (And I’m currently in France for higher ed, so I’m nowhere near that bookshelf. Hahaha.) In any case, the highest levels of fluency usually only come with a lot of personal effort e.g. newspaper reading, dictionary reading, conversation practice, so a textbook probably isn’t as essential.
PS: personal question, even though this thread really should be about you:
Could I ask what sorts of companies you’ve spoken to or found interesting? Any names? And what sort of conferences were you at? (This is of course only if you’re able to disclose such information and are comfortable with doing so.) What I’m actually doing in France is preparing for a bioengineering degree – I’ll be sitting a battery of entrance exams next month to see what schools I can get into. Assuming everything goes well, I’ll enter one of the top schools and graduate with a master’s degree in engineering with a focus in bioengineering in about 3-4 years’ time. (Don’t mind the weird degree title, because the top schools in France all say they’re ‘generalist’, so you’re an engineer first and someone with specialised knowledge second.) One of the countries I’m really interested in after graduation is Japan – I might even apply to do a second master’s degree there, because some schools in France encourage their students to do an additional degree, particularly if they want more focused or applied knowledge. I’d like to work in the pharmaceutical or biomedical sectors, but I have no clue where to start getting information about those sectors in Japan. Would you mind sharing what you’ve learnt?
On my end, I hope there are other ways for me to help you, so don’t hesitate to ask more questions. My approach to Japanese might be a little unconventional though, because I grew up speaking English and Chinese, so kanji was one of the things I didn’t have to learn when I started.
EDIT: I second @OikawaTooru’s book club idea! Reading as early as possible is a good way to get exposure, see grammar in action, and pick up new words and structures. There are some books that manage to use a lot of descriptive vocabulary without being too grammatically challenging, so they’re good for people starting out. Kiki’s Delivery Service is one of them. (The book club is doing a re-run in June, I believe. You can always drop by to spectate if you’re curious.) I’m also part of a ‘learning through translating’ club on the forums: we’re currently working on NHK News Web Easy articles in one thread and on a manga in another. (The manga home thread is here with a story summary.) Most of us were beginners when we started translating, and many of us still are (advanced beginners, perhaps, but still beginners ). The idea is to try to work sentences out with some guidance from more advanced members while picking up new vocabulary and grammatical structures.