We've had a few decorators round to quote for painting our bedroom. Two were happy to use the Dulux one-coat paint I'd bought (tester pot) and quoted for one day's work. The third said the one-coat stuff doesn't look as good and advised two coats of normal paint and quoted for two days' work at almost double the cost.
It would be a cream paint over white walls so I'm not worried about colour coverage, but I've heard that the one-coat paint is much thicker and can look patchy.
I've used Crown Solo (a one coat paint) in the past and it hasn't looked at all patchy. It was a pale gold type colour. I wouldn't use the colour again (I don't know what I was thinking actually) but the coverage was fine!
You are mostly paying for labour so yes it would be double the cost. Woodwork can take ages to dry for a second coat so prob two days is reasonable. I thought the One Coat stuff was over rated and expensive and ended up applying two coats for a brilliant white finish over magnolia walls. Have never used colours so can't comment. Personally, assuming you don't want to do it yourself, I'd take the advice of a professional. Pain in the butt to have to empty your bedroom out twice. Get them to quote for the job, stating minimum two coats of high quality wipeable paint --learned this the hard way--; base + two coats for woodwork; and all sanding and making good. Then they can work as quickly as they like.
I recently got quoted £675 to paint two bedrooms as apparently it was going to take a week. I was so shocked that I decided to do it myself. Yesterday I painted one of the bedrooms, I gave it two coats and it looks AMAZING. I did the first coat at 10am and the second at 4pm.
So anyway I digress. Dulux One Coat is a pointless false economy.
Oops, I was getting confused. I was thinking you were only talking about the. Emulsion One Coat. Hence my comment about two coats of paint not taking a whole day extra. . An extra coat on the woodwork plus the walls wouldobviously take a lot longer.