As the most stressful part of your journey will be the train journey, I would like to be leftfield and recommend a 2 speed Pacific Carry Me. No it will not ride as well as all the lovely bikes mentioned here, but if your journey to and from the station is a shortish one, it will give you stress free commuting

It packs up into a small walking stick shape which you can wheel along very easily. I have the Dahon D3 Curve (nice bike) but think I still may get a Carry Me for a stressfree life