Circa/Rollabind cover material, or A4 covers

I'm in the UK, and seeking recommendations for what material to use for Circa/Rollabind notebook covers, or for a source of pre-made A4 covers. I have a Rollabind desktop punch, and any material for home-made covers needs to be "punchable" with that.

So far I'm using the cardboard backings from some A4 refill pads, but I'm hoping for something stiffer and, hopefully, better-looking.

Advice gratefully received...

aef