mickey my 14 year old yorkie lived in a condo his whole life. 1700 sqft to be exact (well from what my parents say...)
he did fine
he also did went on two walks. one 20 mins in the am, and 1-3 hour walk in the evening (depending on how he felt sometimes if he was tired or didnt like the weather he'd start heading home earlier)
i cannot of course speak on behalf of mickey however he didnt seemed to be bothered living in an apartment.... (because we took him for walks)
the whole time he's home, he always stayed in my mom's walk in closet (much smaller than the whole condo) so we kind of called it mickey's home :P hehe
hope this helped