friutsalad either delux trade or one of the DIY sheds, probably got some good reductions on at the moment, but with all decorating, its all to do with the preparation so get yourself some sugar soap and sandpaper plus a cork sanding block if you don't have any in.
I wouldn't worry about it, Fruits.
Of course, you can never go wrong with Dulux, but the days of the "big sheds" selling diluted inferior paints are long gone.
If 20litre tubs are a bit much for you, then, as Tony says, go for the offers wherever you can find them.
Pro decorators will always have their own preferences, but it's all pretty good these days.