My name here is my pen name. My last name doesn't seem (to me) that it should be hard to pronounce, but it's uncommon and very similar to another, more common last name. In the end, people mistake my last name for the more common one. (This has actually caused some issues with me accessing my child's medical records at one point.)
In addition to the difficult last name, I also want to get into writing more "adult" fiction, and I don't really want anything to easily tie back to me as an individual. Wade and Ferry (the F. in my pen name) are both easy to pronounce, not super rare or super common IMO, and are further up on my family tree. There's only so far I can go up my tree due to poor family records (such as an orphan ancestor whose maiden last name I don't know), but I think it works pretty well.
Other ideas are to use similar names (like what @Celia does) or use part of a last name from your family. E.g., if your last name was Smithson, you could use Smith, Swift, Stone, Smitty, Smyth, Smythe, Smythson, etc. or vice versa. In this case, you could have a full pen name: Sonny/Sunny Swift/Smith/etc. You have a lot of options. Feel free to post some you're considering here, or ask some of your writer friends for feedback on how the names you come up with sound and read.