When I entered 'book cover design' into google the first thing the popped up was canva.com
The site lets you design a cover and at the end you simply buy the photos or use of them from the photographer who uploaded them. You can browse their templates and while there were a lot I did not see many any that fell into what I would see as urban fantasy or science fiction. IF I could find photos or designs of my own to use I could upload them. So it doesn't completely rule them out.
The next site was the website "Creative Penn". This isn't a design site but an article on the topic. The author of the site Joanna Penn a thriller author with New York Times best sellers, suggests in her article that you get a professional designed book cover, especially if you are a new author. While not the same genre, she has a point. A cover of a book is what catches the person's eyes enough to get them to read the blurb or even buy the book. I know for an author I have never read before the cover is what catches my attention first. Ms. Penn also offers courses that I plan to look at later.
Of course if someone chooses to go through Amazon to publish they have options for design as well. You can upload your own images and there are also stock photos. The downside right now is that you have to be ready to publish in order to see their stock images.
Other sites such as Create space also have ways for authors to create a cover. I think it may have to be a thing I decide after I decide how I am going to publish. As I said I am leaning towards self publishing I just don't know who I will go with.
I think I will be doing more researching on that. First and foremost I need to edit the book. That I will definitely be looking into professional help with that.