Keeping home workouts challenging with only adjustable dumbbells

I train at home with adjustable dumbbells, a bench and not much floor space. Rows and pressing are easy to progress, but lower-body work feels limited once the weights stop being challenging for squats. I'm experimenting with split squats, slower lowering and pauses rather than buying more equipment immediately. What variations have kept home sessions genuinely hard without turning every set into fifty repetitions?