Switching to larger bottle... Annoying!

My LO is 11wks eats 3-4oz every 3-4hrs except at night when she'll go 5-6hrs without eating. Lately she's been acting like she could eat more after some of her feedings but not all of them. The bottle I use is the Dr. Browns 4oz and I hate the idea of going up to the giant 8oz bottle just to give her 4.5-5oz. Why can't they make a 6oz bottle??