I used 5/4 cedar boards (sold for making household decks). The boards were inexpensive, available in fairly long lengths (16 feet), and measured an inch in thickness. Handpicking got me the ones which had the smallest knots. The wider strips don't bend easily in the 1 inch direction, but "cheater" strips help fill the gaps.

Or, you can easily rip the 1 inch strips into strips that are a bit under 1/2 inch, or go down to 3/8 by 1/4 inch strips. These look like very long pencils and will bend almost as much as you would want in any dirction you might choose.

Years ago the cedar strip canoes used strips 2 to 4 inches wide. There were fewer strips to fit, so the time needed to produce a boat was less. If you wanted to try the same techniques with modern materials you could use a bandsaw to resaw 4x4s or 2x4s to give you 3.5 inch wide stock, or you could cut strips from a sheet of plywood and have nice even strips with extremely uniform thickness.

PGJ