When I had IBS symptoms I adopted the FODMAPs diet (Google it) and found it had almost immediate effects. Colonic hydrotherapy is another option, although many people debate its efficacy. It didn't do much for me other than temporarily remove the bloat. However, given it's widely available, low cost, and a one-off session is all you really need, it's worth considering as a useful 'clean slate' strategy and may benefit all types of subsequent nutrient take up.
Since the episode above, I always supplement with probiotics and digestive enzymes but doubt they would do anything had I not done FODMAPs for a couple of months.
Last thing I'd say, in terms of carb intake, which you were worried about, opt for rice (steamed Thai or jasmine is my choice). Rice has an incredibly low allergy rate.