I concur that a great instructor/swing coach is invaluable. I would recommend asking on the forum if anyone is in your area and if they could recommend a coach and what they specifically like about them. See if what they like matches your criteria. After using 2 "mediocre" coaches, @klineka recommended a coach locally that I am very happy with.
That said, you have to be committed to the priority piece the coach gives you from lessons. This and incorporate the 5 S's during practice and you will likely be amazed with your progress. I started practicing this way mid-season last year and have made considerable progress.
It still baffles me when someone in the practice stall beside me shows up after me with a jumbo bucket, 175ish balls, and finishes well before me hitting a bucket of 75 balls. As stated in a previous post, raking and hitting balls for the sake of just hitting them will not help much, if at all, other than to further ingrain bad habits.
Good luck in your search and progress.