I'm in the same boat right now looking for alternatives.
What I know I need includes:
Wiring including amp control and canbus decoder (basically any box on the steering controls seems to be fairly universal fit).
Seen some recent ones actually offer a connection to the phone controls, though how honest this is
Brackets.
Facia adapter because its not actually a double din (which is 7 inches, the gap is actually 8.6").
If going bigger than double din, being aware it'll likely interfere with the cup holder as it sits proud of the dash.
I have the full speaker system, but no CD player that I know of aside from the head unit.
It does beg the question if it will work.
Did also consider self build, but think I would struggle to match off the shelf products.