Blonde again

I am thinking of returning to my childhood, when I
was a tow-head. Of course it gradually got darker
over the years. It is now probably a light to med.
brown (with alot of gray). I have been coloring it
a light auburn to strawberry blonde for the last
8 years. I would like to be a medium blonde, I
think it would make the gray less noticeable. The
store bought stuff just won`t cover anymore & I
need a change. I would say I`m about 30% gray.
Thanks!