Some thoughts...
A tissue valve isn't apt to require warfarin, and should have little effect on your unhappy midsection. However, it will need to be replaced, meaning another surgery, and the risks associated risks with it.
The Ross Procedure may work for you, but depends on what shape your pulmonary valve is in. That can vary in people with bicuspid valves, dependent upon whether there are other tissue factors involved at a level that would affect the tissue of the pulmonary, or if there is a tendency toward aneurysms.
Mechanical valves will likely keep you from further surgeries, but the warfarin is a risk factor to people with gastrointestinal issues that can invovle bleeding. Internal bleeding can go undetected long enough to be dangerous, and it's difficult to determine volume accurately. Some people don't seem to change their bleeding habits very much on Coumadin, but others do bleed more easily and stop more slowly. You don't really get to find out which one you are until you've made the leap.
Ulcerative colitis is generally considered an autoimmune disease, along with psoriasis and most forms of arthritis. I don't know if there are interactions between warfarin and any of the newer treatments now in play.
If your colitis may require surgery later on, Coumadin adds to that risk. It will also require bridging for the type of exams you're undoubtedly treated to at least annually - again a risk.
Unless an overwhelming x factor pops up, you will need to determine which risks you tolerate best in life, and be guided mostly by that.
It's never simple.
Best wishes,