I actually bought bought a white cotton sheet,180 thread count,on EBay as it was cheaper than buying fabric, then bought a metre of cotton waffle and used Hobbs Heirloom wadding. Lemon binding is cotton seersucker.
I had 100% cotton white fabric in my stash, but it felt too stiff for the purpose, so that's why a sheet seemed a good idea, except I now have lots of fabric left!