Re: Keeping it going over Christmas
So you're supplementing with about 3 oz of formula per day, and 4-5 oz of expressed milk? That's really a small amount of supplement, and I think you're really, really close to being able to phase out the supplementation and the SNS altogether. In fact, I'm willing to bet that you could stop supplementing now.
I know it's really hard to keep up with a demanding pumping/nursing/supplementing routine when you have family in the house. I hate to say "Suck it up and deal" but you're SO close to getting the supplement/SNS/pump monkey off your back that it might be worth it, even at the cost of a not-so-much-fun Christmas... But that's easy to say and hard to do. If you want to dream-feed your baby, I'm sure that would help reduce the amount you need to supplement.
One other thing that might really be helpful would be to get your husband on board with your breastfeeding goal, so that if you retire to the bedroom for a marathon feeding session and people start getting snarky, he can stand up and say "Hey, elelou is working incredibly hard to do what we both feel is right for our child. We might not be doing things the way you think they should be done, but I need you to respect her determination and not say things that will make her feel bad. She needs your unconditional support right now."
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"