Quirite didn't catch the subtle satire in my comment.
In any case. If your son is a PT and is going to have an internship in Gavinana (a town in the province of Pistoia), chances are he will be working in one of the Rehab centers of the Turati Foundation. My aunt went there in the last years of her life.
I presume they will give him the uniforms or scrubs. If not he can ask where he can find them. The medical uniform worn by nurses or therapists is called "camice da infermiere". Therapists also wear a sort of uniform jacket that is called "casacca medica". I know the area as my aunt and uncle lived near, but don't know of a specialized store that sells those uniforms. Google the words above and maybe you can find something online.
For regular clothes in Florence at the San Lorenzo market there are plenty of choices. Or on the West side of the station, on via Alamanni, there is Santini, a reasonably priced store that sells everything from jeans to business suits (that's where I buy my business suits).
However Gavinana is near Pistoia. That entire area from Prato to Pistoia is where the Tuscan apparel industry is (now mostly Chinese owned). There are plenty of even cheaper places there. Just tell him to ask his colleagues.