Custom Permalink

Hi,
I’m using this custom format of permalinks /index.php/%category%/%postname%/

But, this is not recommended by WP due to performance reason, so i need to start it with a number, i don’t wanna start it with date or post id, as it is for a website, not for a blog.

I wanna keep the format like this /index.php/number/category/postname

any help please.

regards