Thanks for the comments and helpful feedback on what fabric to use for dyeing. I have found two useful sites which seem to have the best variety of calico and Prepared for Dyeing (PFD) muslin.
calicolaine sell a variety of different weights in Calico
I have gone ahead and bought a selection of all of these and will try them out to see results.
Now all I need is some dye and a book to help along the way.
- Adventures in natural fabric dyeing (collectmeblog.wordpress.com)