good luck emma, unfortunetely here bottles make no difference to sleep, even when they got formula in, but haven't tried any for ages. All I know is DD1 managed to wake every 2 hrs for her formula milk! And E sometimes drinks very little when she wakes and still goes her normal 3 hrs and then sometimes she has lots and up an hour later, I read this really interesting book by William Sears regarding babies sleep.
I am so scared of sids I am happy for her to wake every 4 hrs. But anything less than 3 hrs is really too short for me! As it takes 30-60 mins until she is down again with nappy, drinking, winding and then going back to sleep!
Off to boots for some more bottles then!