For my specific laser and use case, I don’t need sublimation paper. I just make sure that I use light color keycaps made of primarily of PBT (not ABS!), I cover the entire keycap with a Cricut infusible ink marker, and then I find that a very low power setting and moving very slow gives me almost no “overspray”. On these two keys, which look a bit better in person than in that zoomed in photo, I made a point of cleaning with isopropyl alcohol first, and that seemed to help.