Best material to use for basement floor.

I'm working on a friend's house in the basement putting in a 3/4 bathroom. We had to break up floor to install the drainage system. The area is approximately 10' long with varying widths. (Pic included). What's the best bag of mix to use and should we add a hardening or strengthening additive? Would sand mix or mortar mix be ok? Don't really want to use concrete mix because I think it would be to difficult to smooth area around ejector basin. Now the area around basin will be in the utility room with 1"gap between it and wall. There is 40" area in the middle where toilet flange is. 20" from center of toilet to a wall on both side. That is the only area that will have direct foot traffic but minimal. The remaining ditch where pipes are sticking up will be under a home made shower that has pan liner, mortar base, backer board, and tile.
. I appreciate any suggestions.