Domain names cannot be replicated. If one is taken, the only recourse would be to approach the owner to discuss a sale. While there are other variations you could choose, sometimes owning a certain domain (especially if it is attached to your business) can be worth the premium. Often, people will scout out domain names that are still available, buy them, and then sit on them in order to sell them down the road. Depending on who may want the domain down the road, you could sell it for a large markup.
I no longer count traditional publishing as passive income because after you’ve spent half a dozen years pitching agents, arguing with publishers, and having your heart broken repeatedly only to make about a dollar per book, it’s not really passive income. More like overdue income. The responsibility that traditionally published authors shoulder is much too high and the cut far too little to make this even a profitable, let alone passive, income option for most writers.
Also, I know from my personal experience that when you only do something because you think it’s a money-spinner you end up nearly killing yourself to get the idea over the line. I remember creating a careers advice site that bored me to tears. Every word I wrote, hurt a little. All 200,000+ words! Do not put yourself through this pain. I know I won’t ever again.