Designer paints like Farrow & Ball are nice to look at, but horrible quality.
Dulux is the best all round paint. Dulux Satinwood is a very good paint and finish for interior wood. Sikken's wood paints are better quality again and the only paints to use if you insist on using water-based wood paints, although they do oil-based versions also - Sikkens do not make wall emulsion, but they do make the very best varnishes and stains.
One coat or self-undercoating gloss is not new to painters who have been mixing a bit of undercoat in with the gloss as a cheat for decades that I know of. Always has been a bit Mickey Mouse and I wouldn't touch it or employ any decorator who proposed using it.
Some paint manufacturers that were good 30 yrs ago aren't so much now, Crown and Macpherson for example. Permoglaze emulsions quite good, Leyland microporous, Johnstone interior emulsion a good cheap alternative, but not their exterior masonry paint.
Synthetic brushes are popular nowadays, though personally I find the bristles too coarse compared to natural bristles - their only use for me is as a cutting in brush for emulsion as the ends are cut perfectly straight and I always flatten my cutting in with a 4 inch foam roller.
Dulux make a 'trade' version of all their paints and emulsions which amounts to a more concentrated version of the retail version. It is only really worth buying the more expensive trade version for exterior work or the Dulux 'trade' Satinwood on interiors is wonderfully easy to work with.