In that case, welcome. Here's a complimentary notice informing you that upon asking any suggestions for a full UI package that everyone in this forum is going to rush here and say two things repeatedly even if they've seen someone reply with their own suggestion. However I'm optimistic, so here they are. Here's hoping no one else suggests them.
1)
TukUI
2)
ElvUI
Now, as for my own suggestion I'd say neither of those and build your own using some of the following (all are available through the curse client);
1) Bartender, Dominos or Macaroon for Action Bars.
2) Anything but X-Perl for unitframes. I know there's a devout following for
Shadowed Unit Frames.
3) You'll probably want Grid + Clique, Healbot or Vuhdo if you ever intend on healing, but you could probably do just as fine without them.
4) kgPanels for backdrops and artwork.
5) MoveAnything (thanks to deepfriar for reminding me on that one)
Those are the absolute basics if you want to build something quickly yourself, the benefits of doing so are that you're not going to be limited by what someone else thinks a UI should and should not have, as is the case with virtually every UI package in existence.
Downsides include it not looking as pretty unless you're willing to spend days on perfecting it, and you might end up hating it and redoing it a couple of times before settling on something.
Oh and to answer your question, I don't think you can get it via the curse client.