What size plastic bed

I am a new Staffy owner buying a bed before adult female dog arrives. Bought a 70cm plastic bed (Pets at Home Large) with padded insert feels a wee bit small but probably Ok when she is asleep. Any opinions on the perfect size.
many thanks

Hi, the image below should give an idea of the size of Rockys bed, he is an adult now although you wouldn't believe it seeing this picture:



Please come and say Hi, we would love to know more about you:

https://staffy-bull-terrier.niceboard.com/f7-new-member-introductions

Thanks for that, funny as size of Roxy's bed doesn't seem to be an issue for him or relevant! Will put up some photos when we get organised with new family arrival.

Darcy has this one in large

http://www.petsathome.com/shop/en/pets/dog/dog/dog-beds/rspca-faux-leather-dog-mattress-in-brown