22 year old young professional looking for a Lisbon room

I'm a 22-year-old American young professional--I will be working at the Universidade de Lisbon next year--looking for a shared flat. I'd love something by Marques/Avenida so as to get to work more quickly, but something nearer to the city center would also be fine.

I don't smoke, don't have any pets, and am looking for a reasonably relaxed but social environment. I speak Portuguese well and would prefer an apartment with at least a few Portuguese speakers, to get a fair amount of language practice. I have lived in Lisbon before so am looking to feel at home, have a comfortable place to work and play, and meet some great people!