Proper Microphone for Indoor Use & Filter out Ambient Noise
My two suggestions are:


Use a lav mic and don't worry too much about a small mic being visible.  Training videos don't have to look like Downton Abbey.
Use a shotgun mic, but also use an acoustic absorber behind the talent.  It is true that all the ambient noise that comes through the walls will bounce around the room, and if you don't have an absorber behind the talent, the shotgun will "see" the echoes of the ambient noise coming from behind the talent just as much as it "sees" them coming from everywhere else.  But if you can deaden the back wall, the shotgun will "see" a quiet wall with talent in front of it and can filter the noises coming from everywhere else.  The closer you can get the shotgun to the talent (using a boom) the better.