650c wheels bicycle (for 5'3 and under)

Ed, I was thinking I'd like to be a bit more upright (and, therefore, more visible to drivers) in London traffic given my titch height.

In all honestly, cycle training would make you feel more confident about being visible to other road user, a small increase in stem height will make you feel more confident, but as for being more visible, that's down to your road positioning rather than the slight increase in your height.