As it is, I realised others might be in the same situation as me and so I thought I'd give some recommendations of stories I read that I thought were fantastic. I'm not much of a reccer, so bear with me (or, if using my usual spelling - bare with me, wooo!)
All of these are primarily gen, because, if you hadn't noticed, I ♥ gen fiction.
severa's New Habits Die Hard [G] - a missing scene from 2.08 that is heartbreakingly realistic. I've adopted this as part of my personal canon. It's the scenes we needed in the show.
m31andy's The Man Who Sold the World [PG] - a post 2.08 fic that works as a 'fix-it'. It's beautifully bleak, with a keen insight into Sam and the position he now finds himself in.
bistokids' Life Before Mars Part 1 & Part 2 [PG] - a pre 1.01 fic that provides backstory for Sam. This is believable - terrifyingly so - brilliantly rendered, with some very tight Sam characterisation that works.
yunitsa's Subjective Idealism: Five Things at the End of the Rainbow [PG] - a glimpse at five alternative endings of Life on Mars. Each of the endings says something about the show, the characters, and reality.