Oh bless!
I think if you look you will find similar posts from most of us when ours are around that age.
Great advice from bizzylizzy, I did and still do lots of brain training with Reese, as found he had far more energy than his age related walking time allowed. He loves hide and seek, I put a treat in the little puppy kong he had, make him sit and wait. I built up making it quite easy to find at 1st but now can hide anywhere in house or garden and he doesn't stop until it's found , which sometimes can be a while!
At that age though it's also making sure they get enough rest, I used to find Reese would get more mouthy and a bit mad really, when he was actually tired and needed a nap.
It was quite easy for me to establish a routine as it's just me with him, but routines are good.!
He goes to my mums when I am at work and we had quite a few problems with her dog. She hated him for about 3 months and would growl as soon as he went close, but now they are best friends.
As for the constant monitoring, well I am still doing that. I have made home and garden as puppy proof as possible, however I have taught leave it and give it which has helped my stress levels a lot.
Hang in there, it does get easier!
Tracy & Reese