If you want to do a deep dive into "popular paperbacks of the 80s and 90s," the Sweet Valley Twins were just as popular as the BSC back in the day. (Just ask your mom, cool aunt, and/or local librarian.)
This is actually my #1 Baby-Sitters Club readalike suggestion! It has all of those "friends starting a business" vibes only with dog walking instead of babysitting.
Have you ever struggled with feeling like you don't have a group to belong to? This one's for you.
While the focus is more on friendships (and rivalries) than the clubs, this series has a lot in common with the BSC!