I make my own knotted leaders. They have a formula for making each size. As I loose the tippet I just tie on the same size as the last piece. You will need to learn to tie a Blood knot. I have a blood knot tying tool that makes this easy. I bought it from Orvis. You will loose some as you switch flies so you will need to add some to your leader. If you don't want to add tippet to your leader you will need new leaders. A blood knot looks hard but it is very easy knot to tie with a tool. Here is the tool that I have,
Blood Knot