this is tough!
i have struggled with this a lot! now, i differentiate this process. i teach second, so i have a huge range of readers! we go from level E to level Q in my class, so it's unrealistic to assume book shopping would be one-size-fits-all.
i used to have Monday as my shopping day and would have kids shop for 5 just right books during their centers. I noticed that it really only worked for a handful of kids. for example, my lower readers (levels F, G, H) need more than 5 books and they need a lot of help picking! my higher readers (O, P, Q) need less books and less help.
so, now I do my just right book mini lessons at the guided reading table, where i can show them what books are right for them and about how many they should have. As kids get higher and more independent, I let them switch books mid-week if they need to.
when i conference, i always peek in their book bins to see how they're doing. usually they all need more nonfiction and poetry, but we're getting better! many of my conferences involve shopping with the kids- getting them excited about books and showing them how certain books can help them.
it's really un-authentic to stop thriving readers from getting a new book...and it's sometimes unrealistic to trust that kids, especially 7 year olds, really know which books are right for them, as much as we teach them. i am 100% behind student choice, but sometimes they need a helpful nudge in the right direction (and a teacher to make a book sound exciting!).