Welcome to the forum Trym.

First, your Sim's apartment is the only one in the whole block, so to speak. It is not like The Sims 2 Apartment Life, where you could have four apartments in a building. An example is in the Apartment Block in Bridgeport called "One Leo Center" or something similar. On the second-to-top floor, there are two rooms designated as apartments in a 4x4 space. It's pretty much impossible to fit everything a Sim needs into that small a room.
Second, There is a thread
here that could help you. It describes how to build an apartment from Scratch, however you can use that guide as a base to renovate apartments.
I hope this helps.