I would refinance with a different company and stay in the current house.
When I was pg with our 3rd, I had the same thoughts. Our house size is close to yours. Since #3 was born, I cannot tell you how many days we have all been sitting on 1 couch cushion. We really do not need more space - all 3 kids are usually in the same room, anyway.
What has helped us is storage and limiting objects in the house. After number 3 was born, we set up storage in each bedroom. No toy boxes - just toy organizers and shelving units. We also have 2 toy organizers in the closet under our stairs. Those are the only places we have toys. We go through our toys before Christmas and Birthdays and the kids choose what they no longer want to keep to make room for new.
Another thing DH and I have given up is the whole "no kids in our bedroom" deal. I was never allowed in my mother's bedroom growing up,so this is new to me. Our bedroom sort of functions like a den. We have an LCD TV mounted on the wall above the dresser and the kids are allowed to go in there and watch tv.
When I was pg with our 3rd, I had the same thoughts. Our house size is close to yours. Since #3 was born, I cannot tell you how many days we have all been sitting on 1 couch cushion. We really do not need more space - all 3 kids are usually in the same room, anyway.
What has helped us is storage and limiting objects in the house. After number 3 was born, we set up storage in each bedroom. No toy boxes - just toy organizers and shelving units. We also have 2 toy organizers in the closet under our stairs. Those are the only places we have toys. We go through our toys before Christmas and Birthdays and the kids choose what they no longer want to keep to make room for new.
Another thing DH and I have given up is the whole "no kids in our bedroom" deal. I was never allowed in my mother's bedroom growing up,so this is new to me. Our bedroom sort of functions like a den. We have an LCD TV mounted on the wall above the dresser and the kids are allowed to go in there and watch tv.

We recently found out we are expecting baby #3, which is wonderful news, but a total surprise, and totally unplanned. (we had decided to stop at 2!) Two of our bedrooms are a great size, and the third (currently our playroom) is 13x9.
We can make our mortgage/car pmts fine. Some months might be a little tighter than others, but we're in a good place. I'm trying to figure out, though, how to make our house work for a family of 5.
That's a lot for an addition, especially since we just bought a 2,000 sq ft. house for 80k.