If you want more locks, you’ll have to brush yours out and restart to give yourself a higher number. While having more locks can create the illusion of volume, it still doesn’t change your hair thickness or hair density. Most people are stuck with the volume they have.
There are some slightly effective ways to add volume to your locks. You can do braidouts. All you have to do is braid all of your locks. Then go a while with the braids in—sleeping in the braids at least once is preferable. Take the braids out, and you’ll have great little waves in your hair. If your hair has trouble maintaining a curl, try dampening your locks when you braid it.
If you blow dry your hair, try holding your head upside down while doing so. That tends to give your hair a bit of extra oomph.
Also feel free to add synthetic extensions to the root for temporary wear. The should be removed before each wash, but they definitely add to the body of your hair. Adding temporary wool locks at the root is also an option.
Feel free to extend the ends of your hair, but I would avoid trying to attach new permanent locks on the root. It wouldn’t work as well as some would probably hope. Your only safe options are temporary.