You do not have to use design principles. You can also use Sandoval’s idea of conjecture mapping or Simon’s notion of hypothetical learning trajectories.
Sandoval, W. (2014). Conjecture mapping: An approach to systematic educational design research. Journal of the Learning Sciences, 23(1), 18-36.
Simon, M. A. (1995). Reconstructing mathematics pedagogy from a constructivist perspective. Journal for Research in Mathematics Education, 26(2),114-145.