I went to boarding school then went to college at St. Lawrence. People used to call our boarding school JV St. Lawrence and call SLU Varsity Boarding School.
I would say any small NE college will be similar with all of the ones mentioned above being the most similar to boarding school. I wanted to keep the boarding school feel and I loved SLU, Hobart, Hamilton, Colgate, etc. I looked at Boston College, UVM and UNH but thought they all felt too big for me.
A good friend of Ds went to Taft and said U Richmond felt almost exactly the same. The architect was the same for both schools so they look alike but even the students seemed similar.