Where can I buy cotton drawstring school PE kit bags and how big should they be?

[Cleanandclothed]

I would like to buy a/some plain cotton drawstring bags for PE kit that I can then embroider. This is for PFB so I don't know how big they should be!

thecleverbaggers.co.uk/bags?cat=17 for oodles of colours. You can embroider, sew, fabric paint ... Their 'large' size will be ample.

Thank you!