Im having the same problem except with a tail, a pair of ears, and a collar. Which is obviously an easier thing to solve. But the solutions are simliar. Heres's whatcha gotta do:
Be serious with your parents when you tell them. Don't make it seem like a joke.
Explain to them why you personally want a fursuit.
If you have to explain furrydom, explain it.
If you feel like you can't say it, write it.
Tell your parents that a fursuit would make an excellent gift which is entirely truthful
If they seem like they don't care, keep bringing it up so that they do.
That's all I got for ya. Good luck to the both of us