This used to hit my dad pretty hard.
He is now on a low residue diet, google it. It's a low fiber diet. One approach to treat diverticulitis is to "eat more fiber", which he did at first, but this made his diverticulitis worse. So he was switched to a low fiber diet. If you know you've been eating a high fiber diet and you keep having severe flare-ups, then you might want to ask your dr about a low residue diet instead.
He also eats 5 -6 smaller meals and drinks a lot of water with meals and between meals. At the slightest indication he might be getting a flare-up, he switches to a liquid diet for a few days.
He quit smoking and drinking. I bought him a spinner bike and he's been doing that for exercise.
Re: supplements, I buy probiotics and slippery elm capsules for him on Amazon (see below for non-affiliate links).
Slippery Elm (also used to treat IBS):
Amazon.com: Now Foods Slippery Elm 400mg, Capsules, 100-Count: Health & Personal Care
Probiotics:
Amazon.com: PRO-15: #1 Recommended Best Probiotic Supplement: 60 Once Daily Time Release Pearls - 15x More Effective than Capsules with Patented Delivery Technology - Easy to Swallow - Great Probiotics Supplement for Women, Men & Children - Promotes
I hope some of this info will help you. I'll email him to see if there is anything I missed and if so, I'll post again in the thread.