Roots brand (Canadian, but ships to US) has a large wallet with a check book cover in it, too, though I suspect you can substitute your own. Dont have website handy, it is a large clutch wallet... v nice quality, I have it in red.
Roots.com, I have the 'large clutch with in China Red - I see there are more styles than when I last looked. What is nice is, the check book holder comes out of the wallet and it also has another driver's license window and more than a couple card slots, can just throw that in your purse if don't want to carry the large wallet at times.