If one Newf could provide so much love, can you just imagine how much love you'll get from two?!? I'm truly in love with the breed and cannot imagine now what life was like before we had a Newf.
We only have Rosie right now too, and have also considered getting a puppy to keep her company. I would agree with the others that it's a huge financial responsibility, we already had a taste of that with one Newf, when Rosie tore her ACL and needed TPLO surgery. If we got a second dog, I would hate to be unable to provide the same high level of care for one or both dogs just because I couldn't afford it. It of course also takes more time to provide all that Newf attention (Rosie expects at least 30 minutes of petting in the morning). I think a second Newf is definitely a big decision, but if you can weigh your pros and cons, you might find it's well worth it!