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Stop beads running round the bottom of the room probably. They're similar to a corner bead but have a single raised lip that provides an opportunity to finish the plaster neatly and in a straight line (assuming they've been tacked on with a straight line).
You then have the option of putting them on flush to the floor or with a shadow gap which will help hide and variation in floor height.
Also becoming more popular these days is skirting and architrave that sits flush with the face of the plaster. Again this uses stop beads to achieve the desired look.
Its worth noting that both of these requires the hiring decent trades as, with any simple looking finish, it's VERY easy to get wrong and will look shit if it is wrong. This makes it significantly more expensive to achieve.
*We've got a friend whose husband is a fairly well known architect. He absolutely hates skirting boards and in their big victorian house he got rid of them all. I'm thinking we might do the same with our next place as I've realised I'm not a fan either, especially as Victorian skirting seems to have been designed with a gap at the bottom to let mice in.
Good call on the stain by the way! And I also like your curved coving.