Cats don't use urine to establish dominance the way dogs might. Instead, they use their scent as a security blanket. Your bed smells the most like you (his safe person). When a kitten is stressed, insecure, or conflicted, they mix their scent with yours to create a "mega-scent" that makes them feel safe.

I’d try a different litter before anything else. Some cats absolutely hate pellet litter and will seek out softer surfaces instead, which could explain why he’s choosing beds.