How slim is slim? That is a relative terms. There are many slim RTW shirts, some more than others. What is your size or measurements? Which ones have you tried? These answers will help people provide answers.
I think you made a mistake in using the blow dryer. If you review the videos on the otter wax site they do not use heat at all. Just apply the wax and they say the friction is enough to have it properly set in. Curing is setting the denim aside for a couple of days in a cool, dry place or in the freezer.
Both well made. CDW will be more expensive. I'd take CDW myself. You can also look at Mt. Rainier Designs (Japanese designed, US fabric made in China but well made). Both they and CDW use 60/40 cloth. Another quality maker to look at is Feathered Friends (US made). From the UK I'd suggest RAB and PHD (Peter Hutchinson Designs). The last 3 makers are highly regarded for functional down products.