The research opportunities at LACs will not be as cutting edge as those of UChicago, but the trade off is that undergrads get all the research opportunities because there are no graduate students to do it. All of the top LACs will have an intellectual atmosphere and abundant research oportunities, although none probably are quite as relentlessly intense as Chicago, not even Swarthmore. If admission to Chicago was a realistic option for you, I first would look in particular at Amherst, Williams, Swarthmore, Pomona and (if you are a woman) Wellesley. All five of them will give you a great education and tremendous opportunities in a smaller setting. Also very good, but slightly easier to gain admission would be Carleton, Reed, Wesleyan, Haverford, Bowdoin, and others mentioned above.
Rice and Tufts are also excellent schools that are bigger than LACs but smaller than UChicago.
I also wouldn’t assume that Chicago would be too big for you to handle. With the house system they use there, it is difficult to get lost in the crowd.