Edge between corniche and wall

Bought a new house and need to paint it but struggling with a straight edge between the bottom of the corniche and the wall.

I used to do it quite well by hand but maybe its this house or maybe old age creeping up but struggling to keep it neat.
Basically ceiling is white and the wall is a few shades darker grey so really shows poor technique.
I bought one of those edgers from Bunnings so going to give that a go or should I just paint the wall colour on the bottom of the corniche and use the curved part as the straight edge.?

I see now why some builders do paint and walls the same colour

You can bring it up the bottom of the cornice a little but you still need a keep it straight.
Give the edger a go or get a Painter on hrly rate to cut in your tops. Or you could try blue tape.