You asked whether the MMR was OK to get while breastfeeding.
According to Dr. Thomas Hale, from Medications and Mothers' Milk, "Rubella, and perhaps measles and mumps virus, are undoubtedly transferred via breastmilk and have been detected in throat swabs of 56% of breastfeeding infants. Infants exposed to the attenuated viruses via breastmilk had only mild symptoms." The lactation risk category is L2: "Drug which has been studied in a limited number of breastfeeding women without an increase in adverse effects in the infant. And/or the evidence of a demonstrated risk which is likely to follow use of this medication in a breastfeeding woman is remote".
That said, I would not get the MMR. It was originally a vaccine for children. In fact, the rubella vaccine poses a risk of arthritis in women who receive it post-puberty (see Dr. Sears's The Vaccine Book).
Again, if you're asking if it's "ok"--it technically is. I would just look into it further and see if it's really something you need at this time--or something that your doctor is recommending, irrespective of your titres.
Good luck!