Actually pregnancy can be great for colitis. My cousin suffers serious chrown disease and all her bowel problems due to chrown completetly dissapears every time she is being pregnant. When you are pregnant the body releases hormones that relaxes the bowel that's why many women have constipation during pregnancy.
I would suggest to go to chat rooms of people that suffer colitis or meetings in your town for people who suffer colitis and maybe who knows you might meet someone. I don't think having colitis is any obstacle to find a man but maybe that would make you feel more comfortable?
Regarding the pregnancy through donor well do more research. Does it requires that you have a husband? How much does it cost? Can you afford? What does your family think? I know that at 30 you feel urge to having a child, I know I did at 30 (i am 33 now and still don't have children and badly want one). So hey you know if you can afford and you will get the support, at least america is a free country.