You can use what's generally known as a URL slug to achieve this.
Add a new field to your table, called "url_slug" or similar. Now you will need to create a slug for each product, and store it in this field.
CI has a function in the URL helper - url_title($string) which will take a string, and convert it for use in URL's.
For example My product name would become my_product_name.
Now, in your method, you can either - keep the product_id intact, use this as a parameter for your method to show specific products, and use the slug for human friendly links, or you can just use the url_slug to refer to products.
Your URL may look like:
www.domain.com/$category_name/$product_id/my_cool_product/$offset
or it could look like
www.domain.com/$category_name/my_cool_product/$offset
with no ID. the choice is yours, but the url_slug may change - the ID won't. Which may have SEO impacts.
Regardless, your method needs to look something like:
function display_product($product_id, $url_slug, $offset) {
// do what you gotta do...
}
You can then use URL's like the above.
You will need to use URI routing as well, as the example above will attempt to look for a controller called $category_name and a method called my_cool_product, which will of course not exist.
See URI Routing for further info.