Jen2727, I'm not an expert, but am BF-ing my 1st, and I really do sympathise, you're in what I think is the hardest time for BF-ing. Or was for me, anyway.
I was fantasising about introducing formula around now, btw. I found when I got to 6 weeks, I was happy enough to keep going a bit longer. And then a bit longer. Personally I found that taking it a day/week at a time was much more practical than making great ambitions... If I thought about BF-ing for 6 months when DS was 4 weeks old, I would just burst into tears and simply not see how that was possible. Really! Now I've got no idea how long I'll bf for, but that's because I'm not really that bothered, it's easy enough and I'll play it by ear. DS is now 5 months, and no longer feeds like a 4 week old, thank god... That said, if I had found BF-ing truly intolerable for a long time, I would have introduced formula and aimed to feel proud of the BF-ing I'd done, not ashamed of the BF-ing I didn't do, IYSWIM.
Great that your DD took a bottle, and good that you can express, as well - I think 1 bottle a day is a very good idea, to get her used to it, but hopefully not make any problems you're having any worse.
Climberchick's advice sounds excellent to me. If its any help, the scenario you describe whereby expressing gives you a little more flexibility and some breaks is exactly what I have now (except for bottle feeding him myself when I'm out and about - breasts are much quicker, don't go off, and it turned out that I was actually fine about feeding in public, contrary to my expectations. Esp when DS is screaming in a public place and I want to shut him up asap). DP does 1 or 2 feeds a night with a bottle, which is a HUGE help - when grannies are babysitting, or DP takes DS out on his own, they feed a bottle of boobmilk.
It takes a bit of organisation, and I've had the odd day of overly full boobs because of oversupply - but it mainly works very well.
I'm sure it's been a factor in keeping me BF-ing. And I think it makes me appreciate BF-ing more. I see how it bonds us when I've been away from my son - how the bedtime feeds now feel special, rather than some awful chore I couldn't get out of. In all honesty, BF-ing for the 1st 6/7 weeks felt like an awful, exhausting trap. Now it (mostly) feels like a lovely thing we do together, that's a bit of mum and boy time, and keeps us both happy. Weird. If someone told me that at 4 weeks, I wouldn't have believed them....