Personally, store-bought yogurts/kefirs/kombucha really aren't strong enough to notice anything in the short run--with the one exception being the Good Belly drinks or the Attune candy bars, both of which are pretty expensive to take daily.
I NEED to take good probiotics daily. Yogurt and kefir don't benefit me noticeably. I've been dependant on probiotics for 7 years. The first year of diagnosis I took the pentasa and imuran till I informed myself. Then I assessed my own unique situation and took it into my own hands which I DON'T RECOMMEND. Point being that my specific diet, exercise, enteric coated fish oil and good probiotics were all I took for 6 years. No meds until this past year when I voluntarily sought out LDN just in case. No, my disease didn't progress intestinally, but sacral ALA joint pain worsened this past year until I tweaked my Vit D3 levels and the LDN kicked in.
Anyhow, it probably depends on matching the right strain of probiotics to the specific part of the digestive tract that's damaged. If I were first starting out trying probiotics, I would go for the multistrain types from an online megaretailer: Primal Defense Ultra, or Jarrow EPS. From there, I would try single strains: S. Boulardii, L. Plantarum, B. Coagulans, L. Paracasei, L. Curvatus, L. Gasseri... My go-to is living streams probiotic, a L Paracasei/L Curvatus liquid probiotic. If I took the aforementioned multistrain brands, I needed 3 a day on an empty stomach. Since switching to this liquid, I take 2 drops 3x a day whenever. Find your own dose. Hell, maybe none them work for some people. All I know is I DEFINITELY need probiotics, not just yogurt/kefir.
I guess, if I had to settle for stuff in the store, I would go for the Kefir. Yogurt can't hurt and plain is probably best. The main purpose of this response is just to encourage you to exhaust these options until you find one that works noticably.