I can only recommend staying at Theo's apartment! Located in a small side street of St Germain it is perfectly situated for getting around but also offers the quietude (facing the inner courtyard) to relax after a busy day. I came for work so it was great to have a small kitchen, too. Unfortunately, there is no more bathtub (but a newly refurbished flat in return). Beware: it's on the top floor and no lifts!
Overall, a very Parisian apartment that is highly recommended