Need a gluten-free recipe!

Hey, so I'm trying to make a blueberry cream pie for a friend who's got celiac disease and needs a gluten-free recipe. I've never done this before, so I'm not sure which flour to use. Do I need a special gluten-free flour, or would almond or oat flour be better? And do I need to add xanthan gum? Thanks for any advice you can give me!

Here's the recipe I have for the pie, in case that helps. I'm planning to substitute gluten-free graham crackers for the regular ones in the crust. For the filling, I'll need to replace the all-purpose flour with a gluten-free flour. And for the topping, I'll need to use gluten-free flour and maybe add some chopped nuts and cinnamon.

To make the pie, I'll start by making the crust with the gluten-free graham crackers and some melted butter. Then I'll make the filling by beating together sour cream, sugar, vanilla, salt, and an egg until it's smooth and silky. I'll gently fold in some fresh blueberries and pour the mixture into the crust. After baking for 25 minutes, I'll add the topping made of gluten-free flour, butter, chopped nuts, and cinnamon, and bake for another 10 minutes. Once it's done, I'll let it cool completely before serving, and it's even better if you chill it overnight!