Welcome to the forums!

Whenever I hear of someone who wants to troubleshoot their diet, I always recommend first that they speak with a Registered Dietitian https://www.veganostomy.ca/finding-registered-dietitian-ibdostomy-tips/

But, I also understand that this may not always be possible for various reasons, so my next steps would be the following:

• Keep a food diary to make a personalized list of what you find works for you and what doesn't. 
• "Fiber" tends to be a broad term. There are generally two types of fiber: soluble and unsoluble. You may find that one type of fiber affects you more than the other. You should be able to find a list of foods containing both and use that to help you when making your food diary.
• "High-fiber" foods tend to be problematic when they are not chewed or prepared properly. As an example, a kale salad may be problematic for you, but a kale smoothy is likely perfectly fine. Process your food (blend, overcook, peel, etc.) and you might have better luck. 
• This article, which is meant for people right out of surgery, should also give you more ideas on "safe" foods: https://www.veganostomy.ca/ostomy-diet-what-to-eat-first-six-weeks/

Because you have scar tissue, it is wise to use caution, but I think that with some experimentation and perhaps the help of an RD, you should be able to find a meal plan that works for you.