Birdson read my mind. Definitely Mesivta Chofetz Chaim fills the criteria that you stated. Their Limeudi Chol has really picked up over the past few years. While your son would be academically prepared for college, it won’t be encouraged. The vast majority of boys go branching after HS, where they spend (typically) 3 years in one of the various branches throughout the USA, Vancouver and Israel. Most importantly, the derech of the entire yeshiva continues to put a big emphasis on middos and mentchlicht. It’s also an extremely warm place with great Rebbeim.
Of course, once your son goes there, it’s likely he’ll become a part of the “cult”. Once guys get “Chofetz Chaimed”, they stay in the system forever, so if you’re dreaming of an eventual Lakewood boy, it’s less likely.