Hi there,
bmilk or formula is the most important part of your baby's diet till 12 mths so you should keep trying with different cups, bottles, spouts etc to get your LO to accept formula if that is the route you choose....
in saying that, with both of mine, (bfed DS till 16 mths and currently don't see the end in sight with DD aged 11 mths, touch wood)....I dropped the 11am feed once protein was accepted and eaten daily and moved lunch a bit earlier, replacing milk with natural yoghurt....BUT I kept up the DF with both of them till 10 and 10.5 mths respectively so in fact they still had 4 milk feeds plus 3 solid meals.
DD now bfeeds 7,3,7 only but has brekkie solids, a snack of fruit, lunch with protein and milky/cheesey dessert/snack, tea is family supper - sometimes soup and bread, pasta, risotto or something else like this......
I work fulltime 8-3 daily and went back after DS at 4.5 mths and this time at 7.5 mths. With DS I was expressing twice a day to keep up supply and have milk for the 10am and 1pm feeds....then the 11am only as I was home for 3pm.....and that was SOOO tough but this time its much easier as DD was older and already weaned off the 11am feed....plus I DFd DD almost always from the breast so didn't need to express for this....
good luck and whatever you decide, well done for getting to 6 mths.....xxx
S x