For me the size of the apartment in and of itself is a non issue. Dog-proofing the space, landlords that may dislike pets, neighbors that may dislike pets, barking excessively - those are the issues but not necessarily the size of the apartment itself.
Both humans and dogs (in general) prefer more space to less space. We all want to live in bigger spaces.
Most people are larger than their dogs so if a small apartment is large enough for a human, it's likely large enough for any sized dog (so long as they regularly get out and get the exercise that their breed and age requires).
