I honestly think that because of my lack of English I'm lost, since I have 3 assistants (Aoi, Yamada and the aunt) 2 pieces of equipment (shoes and discount tag) and I only unlocked Less tall, but I have no idea what else I should do since I feel like every time I play I do the same thing.

bro think outside the box if you think you've missed something drop the quest in the hospital and lady mystery on the second floor and choose actions that you haven't chosen before

Yeah, most secrets do rely on you reading in game hints. If you don't understand English good enough you might miss them.