Thanks guys. There’s a few 3/4 length, mid-thigh lengths from Aigle, Didricksons and Musto (thanks!). However full knee lenths seem to be distinctly niche, e.g Decathlon stadium wear.
This seems odd to me because for centuries men’s long overcoats were a staple, and for women they still are.
Finally on the DryRobe debate, you’ll have to to forgive me and those of us middle of the road chaps who aren’t dedicated followers of fashion, but who also might be self conscious about looking like trendy watersport mums.