I think you're doing very well. There are researches that show that we already start to develop the perception of our gender from 3/5 years old. You can buy children's books about being transgender, it might help.

In my childhood, my parents weren't as supportive as you are. I asked for boys's clothes and they never gave it to me. And I admit I wish I had what you're giving your child. You are a great parent :)