Really depends on the actual structure more than anything. I lived in a basement for years. Also lived in a garage that was converted into an apartment. It's really more about the insulation and such. I never had any real problems. The basement did indeed get cold, but it was small, so I had a single space heater that did the job when necessary. Easier in California, of course, but probably fine where you are as long as someone's put a little work into making the place an apartment. If not, it might be a little harder. Space heaters are notoriously expensive to run, so if the place is fairly large and you think you'll need to use one a lot, might not be the best bet. If it's a small place and it doesn't get super freezing, imagine you're safe.