It sounds like you've put a lot of hard work into this novel. As you go into this new phase of revision, don't get too caught up in labels. People who do this kind of work go by many different names, including writing coach, editor, reader, and mentor. I'll call them editors for the sake of simplicity in this response.
Finding a good editor is a lot like finding a spouse. Not just any one will do, no matter how shining an individual's credentials or history may be. The editor has to understand your intentions, know how to get you closer to them, and communicate these concerns clearly. As the writer, you need be savvy enough about your own work to know when suggestions aren't working toward your intentions. And you need to trust your editor.
An Internet search is bound to result in an overwhelming list of options. How do you know who is reputable? While ads in the back of writer's magazines narrow the search a bit, that, too, can be overwhelming. Instead, start with your writer friends. Ask writers you know if they have worked with an editor in this capacity, or if they know anyone who has. You might even find that someone you know happens to know an editor who does this kind of work. Also, track down reputable writing organizations to see if they offer this service. (Gotham Writers Workshop—for which I often teach—calls this service “Book Doctoring.") Those that don't offer this service may be able to point you to specific organizations (or individuals) that do.
Once you have a short list of options, start doing your homework. Ask for the contact information of past clients and follow up to see what their experience was like. If possible, talk to the individual who will be editing your work. Get a sense of what the editor values and see if that is in line with what you value. Be precise about your needs. This will give editors an opportunity to let you know if they're able to meet them. Also, hammer out the details. Will you be able to discuss the comments with the editor and pose follow-up questions? Will the editor look at brief revisions to see if you're on the right track? Will you need to submit the novel all at once, or in parts? How long is the turn around time? Decide what issues will be deal breakers for you. If you value follow up, you'll want to make sure you work with someone who doesn't close off communication once the manuscript is returned. Or perhaps you're working within a budget. It's not uncommon to spend $50-$70 an hour for an editor's time.
Finding a brilliant editor doesn't mean you're in the clear. And don't get starry eyed over a name you recognize, or a client whose book that went on to do well. While these are great indications you have a reputable, talented editor in your scope, the editor / writer relationship has a bit of uncertainty to it. Start off small. Do a chapter or two first to see what kind of feedback you get. If the experience is helpful and productive, you can commit to the whole novel. This gives the editor an opportunity to assess the situation, too. If she doesn't understand what you're trying to do or doesn't feel like she can help you as well as she'd like, she can beg off without an awkward and messy refund or termination of agreement.
