Rosey a week is fine for 8-9weeks old. The longer they don't go the smellier gas seems to be. Is he very windy? A fully BF baby not on solids you would expect a very soft stool. Its not hard at all is it? Is his weight gain still good? Only you can decide the best option for you and your DS with feeding. In Australia really at the end of the day fed is best weather is breast or formula. We are luck to have access to safe water and formula if that turns out to be the better option for what ever reason. Its hard to say if formula is the answer with the stuff you have said. There is a good chance it wont make any difference or even make his discomfort worse but if your getting to the end of your teather then it can't hurt to try.

My DS is a bit more settled now and doesn't seem to have the reflux symptoms as bad as he did 2weeks ago. He mostly gets comfort from feeding so that's good.