I would suggest starting with making a list of foods and/or ingredients that you find you are able to eat without triggering the UC. This will be including items that are high carb, so you might be able to put those onto the naughty step from the getgo. Others may need testing out. Do you use a bgl meter to test sugar levels? If so, use it by testing before eating something, then test 2 hours after, and if it raises your levels too much then it too goes into the naughty bin. Just concentrate on taking out the big hitters, and get the carb cravings calming down again before attempting keto again.
Then you know what keto needs, so just do it when you feel the time is right for you. We cannot make that decision for you, nor should any physician or dietician. Do it when you are ready.