I’d agree with above.
About 13 years ago I had a 9 yr old dog; decided to get him a friend and went for another large dog, female, but not a puppy; she was around a year or so. He taught her our house routine in short order and they were solid friends for over 4 years.
She sulked after he died, so I got her a 7 month old pal, also on the larger side. Same thing - though he was never quite as perfectly obedient as she is.
Lost the younger dog at 7 to IMHA; by now the old girl was 12 or so; decided she still wanted a companion, but due to her age, I decided to get a smaller dog. He was about 2 at the time, watched and followed every thing she did. Even better, they would play, and due to his 28 lb size (and great respect for her!) there is no chance of her getting knocked over or hurt.
My recommendation is to do it before the dog is too old and crotchety for benefit of both old and new dog. And, give some thought to what might be the best match - ie similar size or breed, something smaller, energy level.
I always seem to go male/female. My old girl is now over 14 (shep/chow mix), mostly in good shape except for hind end weakness. They still play a bit and she loves her walks but I know our time is running out. When the time comes, I’ll look for something of moderate size, and my “little bug” will become the teacher.
I tend to be a mixed breed fan but to answer your question - Both of your choices are nice dogs but if I had to pick, I’d go w/ the Newfie. Based on my small knowledge base, they seem to be a bit longer in the lifespan. I love the look of the Bernese, however.