Sons Clothing Sensitivities

My son will only wear T-shirts and nothing else. He does not like anything with a collar and wears nothing with buttons, and wont wear dress shirts.

His T-shirts have to be short sleeve... he wont wear anything love sleeve, although hes ok wearing coats and jackets during cold seasons. Im ok with him wearing T-shirts but I at least want ways to encourage him expand his wardrobe. Occasionally I can get him to wear a polo shirt. He has one that we save for special events or family functions and sometimes to school.

One time he wore it for family photos but he immediately took it off when we where done and slipped on a T-shirt. Im still happy he would wear it even though its just for a little bit.