At risk of providing too much information, both my partner and I have dodgy tummies at the best of times, even at home, and we both had to deal with some tummy issues when we last travelled to Asia. However, we travelled to Bali in October and this time we took Ethical Nutrients Travel Bug. It is a probiotic capsule designed especially for travel - you take one a day 5 days before you leave and then one a day whilst you are on holiday. We did not have any issues at all throughout Bali or Lombok (and even ate a few "naughty" salads etc, and things you often get told to avoid). We met friends in Seminyak for our last 4 nights and everyone got ill except us, even though we all ate the same things.
So there it is - travel bug, highly recommended!