You know your son best. What you think he needs should receive high priority in making your decision. If you think he needs an all-freshman door for a smooth entry, then you should look for a college with an all-freshman dorm.
I’ve seen so many kids coming home and transferring after freshman year that it has raised my antennas to this situation. What these various students had in common has overwhelmingly been “fit”. I think that you are very wise to look for the conditions that will be right for him.