I also had a sleeve measured at the physio. Some states have a scheme through the hospitals were you can access one garment a year but I've always had to pay. It is definately worth wearing a sleeve as lymphodemia can start years after surgery. I wear mine flying, driving long distances and exercising.
In warmer weather it also helps if my arm starts to feel tight. There are some great resources out there in regards to preventing lymphodemia so I'd suggest you read them and ask your physio.
all the best.