A long time ago there was an article in Threads magazine showing you how to measure yourself using a flexi curve but you do need a long one and the article on this showed several different lengths, they also showed it's many uses.
The normal length we can get in the UK seems to be 50cm. However back in the distant pass there was a lady in Paisley, Scotland who imported American sewing notions, and I asked her if she could get them in, and she did, last time I saw her selling off all her stock on e-bay - ill health had taken its toll on both her and her family. The one she got for me was by Truflex Felexible Curve 40" ( approx 102cm) , it wasn't cheap but it is a useful tool to have in the sewing box.