I need to change my Wordpress site

I need someone to help us with our website. We are already on Wordpress but have had the same theme for about five years and we are ready for a change. It goes without saying that we want the site to be stylish, simple and functional, but I also want to make sure that it does all we need it to do, and that the backend is accessible and easy to use for our in-house digital team. I also want to make sure that we are properly set up with analytics code such as GA and heat-mapping. We have a theme in mind, and a copywriter who will tweak our current copy and fill any holes, but we need expert advice on how to go about it and someone to actually change over from the one to the other.