Borderline Tumor

I recently had a total hysterectomy for a 15 cm ovarian tumor which turned out to be a borderline mucinous ovarian tumor.  I don't believe my tumor was staged but they told me it was incapsulated and removed intact.  My preop CA125 was 8.  I have been told that I have a good prognosis, which I am very thankful for.  My concern is there doesn't seem to be a consensus on what I need to watch.  My doctor has suggested a pelvic ultrasound every 6 months.  Do you have any experience with this diagnosis and any recommendations as to what my follow up should include?
Thank you so much for your time.