What material would you recommend for sewing to the edges of a cape so I can wear it like a harness instead of using snaps or buttons?

I want to wear my Superman cape like Christopher Reeve did, where he would have two straps on the end of his cape that would be tied under his arms and around his back, so when he had his Superman costume on, the cape would nicely tuck under his collar.

What kind of material should I use and does anyone have any recommendations on where I could get some quickly? I live in the UK and I’ve got a comic con on the 16th August