Depending on how much you feel your current stroller needs to be replaced, you might consider getting a standing board that attaches to the back of a single stroller. My son was walking almost everywhere by the time he was 18 months. And you might find that you don't use a double stroller as much as you assume. Or, if you're worried about your daughter running off if she's allowed to walk on her own, you might consider a toddler harness. I always used to frown aupon the "leashes," before we tried one. Our son was so independant that he didn't really care to even hold our hands when he walked. So, we got one to give him his independant feeling, without risking his safety.
All of that said, if you still feel a double stroller if the way to go, I'd probably stick with Graco, so you can use the infant carrier. If you choose a model that seems a bit heavier duty than the current one, it will hopefully hold up a bit better for you.