Hello and Welcome!!
I have not had surgery but from what I hear, it is very worth it. Most people say their only regret is not having done it sooner.
Have you ever tried any of the rectal meds? either enemas or suppositories? They are available in 5ASA (like sallofalk) or steroid. It may be helpful for you. I don't think 2 tablets 3x a day is the max dose for salofalk, I am not sure how many mg each tablet is but some of us take 4200mg when we are flared up.
Did prednisone help control your flare?
have you been getting your levels checked while on mercaptopurine?