Personally I do not like decal flags. I copy the flag onto a sheet of thin (light weight) paper. I then glue the flag around a piece of thread with white glue, and shape the flag into a wrinkled, drooping shape while the glue is drying (white glue gives you a long dry time). The thread nestles right up into the fold and gives you a line to rig. I frequently download images of flags from the 'net- there are many hundreds, including various naval flags. I use my photo editing program to make a reverse copy, then move that copy adjacent to the original image, to give me a foldable (double sided) flag.
Use really light weight non-glossy, uncoated paper if you can find it.