You can use any size Aida you want. The larger the count the bigger your project and bigger your fabric will be. I am doing mine on 18 count Aida because I could not find any 22 count Aida where I live.
To end up with a similar sized finished design area usually you divide the count by 2 but there is no Aida cloth this size so I would suggest either 14-count or 16-count Aida.