I hope you have a younger team working for your best interests, and only take the advice from them. Be guided by your Surgeon and Oncologist and Radiation Oncologist, there are many sites that you can google to get information from here are a couple. Some information that you receive from others on this site is not necessarily correct, or appropriate for you and your treatment course.
http://www.medicalnewstoday.com/articles/255497.php
http://www.cancer.net/younger-women-who-received-either-lumpectomy-or-mastectomy-have-similar-risk-recurrence-and-lifespan
http://www.health.harvard.edu/blog/for-early-breast-cancer-lumpectomy-is-at-least-as-good-as-mastectomy-201301295838
Wishing you all the best with your choice.
Viv