Can someone give me advice on a cake that won't flake?

My mom bought cheapo Duncan Heinz cake mix as I specifically told her NOT to, and as most ofyou know, when frosting that type of mix, it crumbles and gets into your frosting creating lumps. I need advice pronto on how to keep this from happening. My frosting spatula is broken, and I can't go to the store. I can make a homemade cake recipe if you have a good w\one for frosting.