I disagree with this advice and here's why. Even the low tack masking tape (i.e.
https://www.screwfix.com/p/frogtape-painters-delicate-surface-masking-tape-36mm-x-41m/81496) can pull away the paint from the edges of the plaster hasn't been sealed properly (with a properly diluted mist coat after the wall/ceiling has been plastered). By using tape you run the risk of pulling the paint of the ceiling to the bare plaster. This will require you to fill the hole and sand it flat to the existing paint. It's not difficult but it's time and expense. If you use cheap masking tape there is a very high chance the paint will bleed through too.
My tip for you would be to purchase a decent cutting in brush (
https://www.toolstation.com/axus-decor-blue-pro-angled-paintbrush/p52842) and get to as close to eye level to the ceiling/coving on a hop up platform or stepladders. Load the paint on the brush and use the angle to move it in as straight a line as you can. If some goes on the ceiling/coving then wipe it off and start that part again. It takes practice and patience but you'll end up with an excellent separation between ceiling and the wall. Don't underestimate how long it takes to mask up a room, this method is quicker too.
My other recommendation is decent trade paint such as Johnstone's trade covaplus vinyl matt.
Let me know if you have any further questions, I've done a load of painting so happy to help you out.