Yes, our standard and higher plans allow you to use your own URL to "point to" your IndieMade site. You don't have to own the domain before you sign up, but if you do, you can get your new site ready before redirecting traffic from your existing site.
You can purchase your domain from just about anyone, but many of our customers use GoDaddy, because they are inexpensive and because the online instructions on setting it up with IndieMade are good. We're also personally big fans of DreamHost; they are inexpensive and have good support.
Our handbook pages on using your own domain with IndieMade explains the process in more detail.