chocolate chips cookies at 9000 feet

Cook
This is my first attempt at making chocolate chip cookies at 9000 feet.  I did futz with my usual recipe but the cookies still came out seriously flat.  They were super butttery too.  I think they look like chocolate chip latkes. 

Here is what I did.  Anyone have any suggestions for next time around?  Thinking less butter and more baking soda? 

2 sticks unsalted butter

1/3 cup sugar

1 cup brown sugar

2 ½ cups flour

1 tsp baking soda

1 tsp salt

1 egg

1 egg yolk

1 tbsp. vanilla