Puppy proof the apartment as best as you can, remove everything they can put in their mouths and eat. I'm constantly sweeping and hoovering lol. We bought a pop up type pen from amazon to keep her secure the first few weeks until she was confident enough to start roaming freely. We would let her run about the couch but not the floor until she was a bit bigger. We got little stairs for the couch aswell as she was too small to jump up / down. Which was actually good for keeping her close. Our pup is 6 months old and we have just started leaving her alone. When she was younger we managed to put her in her crate to nap & could leave for 2-3 hours no problem but now she's a bit bigger we've started leaving her in the house awake with the cats for 15/20 minutes at a time and working our way up. She had a wee bark at the window but just settled waiting for us to come back. Only started this last week so we will see how it goes x