A button accordion can be an excellent choice because of they are very widely used and the instrument can be smaller for a given number of notes when compared to a piano type accordion.  There are a number of types or arrangements of buttons.  Some accordions are the same note for push and pull while others have a different note for push and pull making them smaller still for the same musical scale.   Button accordions usually have a very small reach for the right hand buttons enabling the playing of runs very fast.