I tried raw for my kitty last year, not for IBD but because her holistic vet recommended it for her CKD. She liked it at first but then wouldn't eat it, unfortunately.
Some members here do homemade raw, which does require supplementing, and also watching the balance of bone, muscle, organ meats. That was way too much for me to deal with; the mere idea of having to handle all of that raw meat made me queasy. On the other hand, the huge benefit is that you can control exactly what goes into the food.
The commercial raw diets that you can buy are frozen and all are complete; you wouldn't need to add anything to them. I don't know whether the big pet stores carry them or not, but if you have a local, independent pet food store, that's your best bet. You'll find the raw food in a freezer. Primal, Rad Cat, Instinct, and Stella & Chewy's seem to be the big brands for commercial frozen raw and are generally the easiest to find. My vet also recommended a brand named Answers. I like Instinct, and my kitty liked the Instinct dry rabbit food, but their raw seems to have a higher bone content than others, which can cause digestive issues, and there was a recent post by a member whose kitty developed hypercalcemia, I believe. You can take a peek in the health & nutrition forum or do a search for that thread.
I also tried a couple of brands that my local store didn't carry but that deliver on dry ice, Darwin's and Balanced Blends.
What I liked about the Instinct was that it came in little nuggets, so it was easy to take just a few out and didn't require a lot of time to thaw, just a few minutes.
I would think that you'd want to change over very slowly, especially with an IBD kitty. I hope doodlebug will see this and be by. She knows a lot about raw foods and also had an IBD kitty.
Just wondering if you've tried eliminating certain ingredients to see if it's a food sensitivity rather than IBD?