Thank you for the replies. The Alaska fares look attractive so will probably go with them!
I did look at Southwest but I was a little surprised by the prices. I tried all the Bay area airports and they always seem to be more expensive than the legacy carriers. Is this normal? I thought they were here to disrupt things? From OAK for example the cheapest fare is $204 on Southwest which is nearly double the Alaska fare. I see you get 2 bags included but it still works out more expensive. The refund of fare difference is interesting but like you correctly guessed I am from the UK and am not sure when I will be back in the US (although we try visit every 1 or 2 years).