I have the 105cm fabric strap from Hermes and it makes wearing my retourne Kelly so comfortable as a cross body. They are expensive, but if you can get one in a neutral color pattern, it makes it more usable. Mine is in a striped pattern of navy, rust, and white colors.(I pair it with my blue indigo kelly) I usually wear that strap with it and save the other for when I want to carry it on my shoulder. The 105cm on me is too long for regular shoulder strap. It is perfect as cross body.
Truth be told, I usually carry my Kelly by the handle, but for times that I need to carry other things, or if I feel safer in places carrying it as cross body, the long strap comes in handy. (Sorry so wordy! It is late where I live and I am getting sleepy. )
You may want to search for the alternative to Hermes strap thread. Sorry, I can't find it right now to cut and paste the link. This will be helpful in your search for the perfect strap if you choose to not get one from H.