Aoi Hana, Yagate Kimi ni Naru Recommendations
Both are yuri, and have similar settings; I think Aoi Hana is the better of the two, granted, since while it is also slow boil, the heroines have a pre-existing friendship to build on rather than the suddenness Bloom Into You goes for.
Both series are slow burn romance between females.
Both has more portrayal of the relationship between each protagonists, and how they thought.
Both has more stories about side characters.