I have already a webpage hosted in dreamhost.
I'm happy with the service, so im considering buying another domain and host it here.
What's the best option/hosting plan/offer to do that?
All you need to do is register another domain. A paid hosting plan here can host as many websites you want. Go to the panel for Registrations and pick out a new domain to register. Once that's done, go to Domains -> Manage Domains and Add a New Domain (fully hosted).