In my simulation, I’m currently using J2 + J3 perturbations (Fx, Fy, Fz) as depicted on this page: https://en.wikipedia.org/wiki/Geopotential_model#The_deviations_of_Earth%27s_gravitational_field_from_that_of_a_homogeneous_sphere
but I would also add J4 and possibly J5 too.
Unfortunately, I...