I just did this in my bathroom, partly to add lights (flat roof above)and partly because there was some naf artex and old water damage. I looked at right angled drill bits and cable rods but couldn’t be bothered in the end. The artex also had a swirls around the center of the ceiling where the rose was and it was always going to look bodged.
It is dead easy to DIY, rip the old down, do the cabling, screw the new boards up, tape with scrim tape and then fill with easifill before sanding and painting. It also gives you the chance to put some extra insulation in the ceiling if you need it.
Unless your bathroom is massive, there should only be 1 or maybe 2 joins to fill with 2.4 x 1.2 plasterboards.
Cost me about £30 in materials, it is a bit dusty and messy though.