Slats sounds like a great idea.
Since the paint edge between the guard and the wall is below the carpet edge it doesnt much matter what happens to it. Oil based paints dry soon enough, but take a few days to cure.
Plus theres no need to paint down that far, just go a bit below the carpet line. Whatever guard you use, tucking it under the skirting (or PB when there's no skirting) clears the carpet out the way, making a very easy workspace.
NT