Is a Subdomain the Best Way For Me to Go?

I have an existing WordPress site called California Travels but want to change the layout using Headway Themes. I'd like to experiment on my full site to make sure nothing breaks. Would creating a subdomain be the best way to do this? What would be the best way to copy my existing site to this test site? I use BackupBuddy so could I recreate the site on the subdomain using that?

Thanks,

Tom