At your size the XS is probably the size you need. The S size will most probably have a top tube that is too long and it is the top tube that is often the compromise with bikes sized like this.

I have a Small TCR but have ridden the XS TCR and the XS OCR....all fine bikes IF they fit. As others have said, test ride it first and make sure they do some minimal adjustments at least with the saddle and bars.

As far as aluminum goes, they ride fine but the all-carbon TCRs are even smoother. Good luck!