I would give it a go if I were you too. just start slowly.

If you can eat yogurt, the dannon yogurt, vanilla, in the big containers is great to keep in the fridge and eat a couple times a day to keep good stomach bacteria happening while cleansing.

I've done colon cleanses before, herbal.. i don't recall them affecting my stomach much, just make you run to the bathroom more than usual.

ulcers would indicate too much acid no? maybe some extra calcium would help, but yogurt is loaded with that also if you can manage it. Good whole food stores usually also sell something called Kefir that is like a liquid yogurt, might be more organic than dannon. wish i could find some here.