organiccarrotcake I am not sure they exist. I think you have to search yourself and take information from a variety of sites from both sides of the debate.
The reason I mentioned Kelly as not being neutral is that her links were exclusively to sites which back up her opinion, and some of them are so in your face that to someone having difficulties it would make things worse.
When I was going through a major guilt trip about, first, the milk not coming in and supplementing until it did (it did, and I bf), and then, a few weeks later having been hospitalised 2 weeks away from DD and on meds and on ventilators and having surgery, so unable even to express my milk in one boob dried up, I tried and tried to find information which woudl lift off some of the guilt of, when I got home, giving her a little amount of breast milk, and mainly formula feeds (she had of course been ff during my stay at the hospital, but latched back on as if nothing had ever happened, but it ran out after a few days!)
And in fact online there isn't much. So I called several independent midwives and had a couple of visits to a paediatrician to discuss the risks in detail. And what all of them came back with was that yes, breast is best, but formula is the next best thing. It isn't poison, if prepared correctly it isn't harmful, and the pressure on women to conform to the exclusive breastfeeding idea is dangerous to the woman (added stress, even PND). And the mother is as important as the child, and shouldn't have to feel beaten up over everything she does.
So as far as the OP is concerned, I wouldn't worry about supplementing or replacing one feed with FF, as it is very very unlikely that any harm will be done, so she shouldn't feel guilty if that's what she chooses to try in order to get a better night's sleep.
Erm, I shoudl have put this in a PM. But having been through the guilt I just don't want anyone else to have to go through it too, coz it's horrible.