If the standard single monitor setup falls short or outright you have two monitors, either a MacBook and a monitor or directly two desktop monitors, maybe they can interest these wallpapers specially designed for this type of configuration.
The folks at TwelveSouth, a company that has become famous for launching a wide variety of products and accessories dedicated to Mac, has published on its website a few wallpapers with panoramic format to adapt to the resolutions of the different Apple computers and that adapt perfectly to create a continuity effect as if it were a single monitor.
On the other hand, the fact that Twelve South has left different wallpapers hanging on its website is produced because it is a way to promote its products and, incidentally, make itself known more if possible.
I've always liked the customizability of the operating system to adapt your image to my liking as far as possible and in OS X from icon packs to wallpapers or the freedom to relocate the dock for example within the screen space anywhere, it has allowed me to configure it to my liking.
Although the variety of topics in this post is limited simply to landscapes, the truth is that fit perfectly with the aesthetics of the system and personally they have seemed very suitable. On the other hand, if yours is already personalization in a "deeper" way I leave you this link in which we give you some icon alternatives as well as a small tutorial so you can learn to change them yourself.