
I would have a seperate area for the pup that you can pop it into when you can't keep a direct eye on them, it doesn't have to be a crate it can be one of the plastic carriers as long as she/he has his own space in safety. Your adult dog will also need a safe haven if the pup gets too much and each needs to learn to leave the other alone at these times.
I bought a 2 ft crate for a new adult dachsie I was getting so she had her own place she could go when things got too hectic and my lap wasn't available, very soon the other 2 joined her but it didn't worry her so I left them to it, now it isn't unusual to see 5 in that small crate.
Don't leave the 2 dogs alone unsupervised for several weeks/months till you are happy that the puppy is safe with your older dog and bigger in size, I have heard so often of the owners nipping out to the bin or to hang out washing and returned to a dead or seriously injured pup because things got out of hand whilst they were alone and no one there to call a halt to things.
How long have you got to wait for the new arrival?