The cheapest solution will be to experiment with your tippet: try a 3X, for example, and see how that works.
Bigger flies require a heavier tippet. There's the "rule of 4". Divide the fly size by four. The number you get is the "X" tippet you should use. For example, a #12 fly would need a 3X tippet. This is just a rough guide.

A casting lesson never hurts, either.