We stayed at Hotel Felix over Xmas. It fulfils none of our requirements, but it was lovely. We all agreed that if we had to stay in Cambridge again, that's where we'd go!
It is down the Girton road, a drive rather than a walk to the centre of the town. We had an ordinary double with a travel cot. I doubt they have family rooms.
And of course you may be way posher than us, but to me it was a "stay in it for the experience of the hotel" type place, rather than a "stay in it because we need somewhere to stay" hotel. Does that make sense?