I think your puppy would adjust just fine without a little brother or sister. While your puppy would probably like having someone to play with, in my own experience, that would not stop the puppy from crying at night.
It all really depends on if YOU want another puppy. Do you think you could handle two puppies at once? Does your work schedule allow enough time for both? The extra poo & pee & food & vet care & training? But also the extra love and cuteness
If having two puppies at once seems plausible to you, and is something you think you want, then I would definitely consider it ... but all in all I think your current puppy just needs some time to adjust and learn.
It took me 2 1/2 years before I was ready to get a second dog after my first because of all of the responsibility and financial care a doggie requires. Everybody is different, though ... You might be ready now to bring in a second puppy or you might find you're a one dog person =)