She is on the mend, got a bad cough, which unfortunatley is resulting in her bringing most of her milk back up, and as such, think her tummy has shrunk.
I was worried that DD was overfeeding, but since being ill the ounces have dropped off her so I am keen for her to start taking 'full feeds' again.
I found that some feeds, DD would eat 6 oz, other feeds she would eat up to 8oz, therefore I made each bottle up to the bigger amount, just so she had the chance to take as much as possible. Means a little waste, but kept her going the 3 hours between daytime feeds.
I also have a dummy (not sure if you are a fan or not), which, if she woke in the night (after starting to sleep through), i'd offer her the dummy and 9 times out of ten she'd go straight back to sleep. 1 time in ten I'd give her a feed (but would do my best to only give half of a feed, so if the bottle popped out of her mouth, i'd see if she'd be happy to stop feeding then).
It will work out in the end. It is a constant worry though, and I thought I was silly writing all feeds sleeps etc down, but actually, this last week, having to go to hospital, it worked well as I was able to confidently tell the nurses exactly how much and how often she usually fed which definetly highlighted how little she was eating (and was staying down) when she was ill.
Good luck, am sure upping the teat size will go a some way to help you, and if not, as you say, you need the teats anyways eventually.