Yep online with QF FF lets me select seat free
Any thoughts on 10D vs 13A?
Sorry, can't help you with this one, since I don't suffer from claustrophobia I can't pass judgement on it.
CW seats are notorious for being claustrophobic due to their layout/design, with,
I suppose, the "inner" seats (i.e. window and middle block middle seats) being the worst. It gets slightly more boxed in when the privacy dividers are raised and you're going to sleep in bed mode (since all you will see are a lot of tall walls).
Aisle seats, I would assume, have a bit more openness due to an aisle being next to them, rather than another CW seat (i.e. another wall).
If you sit in the EF seats (i.e. the two seats in the middle of a 4 cluster), if you keep the privacy divider between E and F open, I suppose that can give a sense of more space. Note that EF are both backwards facing.
A window seat (e.g. 13A) consists of one wall being a CW seat and another being a window. At least this is a row that has a window (row 12 does not have one, although this depends on the type of 777 you get, but this is likely), so if a window alleviates the sense of claustrophobia, this is a good bet. On the other hand, I have no idea how much space exists between the window seat and the window itself, and the curvature of the aircraft may have a narrowing effect if you are claustrophobic. From my view the window seats look rather cosy.
Here are a few pictures to guide you. I sat in 10E, so I'm sorry this doesn't really answer your question. But it can give you an idea, especially w.r.t. the spacing of CW: