Sorry - wanted to write more last night but had to go see to my LO!
I agree that the Ameda Lactaline is a good one. (In the US, the same pump is called the Ameda Purely Yours.) The other one worth trying is the Medela Pump-in-Style, but they cost a lot more and you can't buy them second-hand (a design fault means you can't be certain they've been properly sterilised after the last person used them), so I recommend the Ameda Lactaline. It's been a few years since I had to research this all when pregnant with my first LO, so might be something new on the market for all I know.
With regard to your question: as long as your baby is being breastfed he will be getting benefits from the milk. The higher the proportion of breastmilk in his diet, the more benefits he'll get. If he gets some formula then it does slightly increase his risk of tummy bugs, and getting a higher proportion will increase his risk more, as well as the risk of some other problems such as ear infections and milk allergy. The less formula he gets, the less his risk of these things, so the risk with the occasional bottle, or with a day of formula on your first day back, is low.
One thing to bear in mind is that any risks of formula get less the older the baby is. And the whole reason for having a freezer stash is to try to avoid giving formula, so giving formula just so that you can build up a freezer stash does rather defeat the whole object.
So, if you can't get a freezer stash now, I wouldn't worry too much, but would just leave it and give formula as and when needed when you're back at work (when, of course, you'll have all the milk you pump each day to give him the next day). The drawback of that approach, I suppose, is that if you don't have *any* milk pumped by the time you go back to work then he'll have to have formula all day on his first day, which isn't a huge problem but would be something new for him to have to get used to on top of you not being there.
Oh - one other drawback - can't believe I didn't think of this before as this problem is the reason I logged onto this site in the first place, but does he take bottles?? Even if he's taken them in the past, he really does need to be taking them on a regular basis (preferably daily or nearly daily) to stay used to them. Some babies are fine just taking them a couple of times a week, but my 3-month-old rapidly went from taking a bottle to refusing it when I left six days between practice bottles. So I *would* recommend trying him with daily bottles now, and, if you can't pump enough milk for them, just give him an ounce or two of formula in each one. (Probably the easiest way to do that is by buying those little cartons that you can just open and pour without having to mix - too expensive for regular use, but only 50p a time so if you're only giving him a tiny practice amount each day then that's affordable & convenient.)
Back to the pumping problem - One technique that works well is to put your pump in the fridge with whatever you've pumped in it, then take it out and pump again any time you get 10 - 15 mins free during the day. (If you've got an electric pump then you don't have to put the whole pump in the fridge - just unhook the horns and put those in, then attach them again when you pump again.) That way, those 15 ml quantities add up during the day. If you can get even an ounce by the end of the day, that's enough to feed him as a practice bottle. If you can save a couple of ounces a day for the week before you go back, then that adds up to 14 oz over a week, which is enough to see him through most or maybe even all of the first day.
BTW, I went back to work when my son was four months old, and couldn't pump enough for him. He was through the freezer stash in the first fortnight and was mixed-fed after that. I got very upset about this at first, but he was absolutely fine and the reading I've done tells me that, although exclusive BF'ing is the ideal, mixed feeding will still give a baby most of the benefits of breastfeeding. So this time my aim is just to pump what I can and not worry about the rest. Let's face it - in twenty years time, our babies will care about a lot of things we did or didn't do, but the amount of breastmilk we managed to pump isn't going to be one of those things!
Sorry for the length of this - hope it helped!
