One of the most beautiful things about Yiddishkeit is our diversity even among the frummest Yidden. If you are chasidish, your belief is that you become closer to Hashem through following the Rebbe’s advice to the T, since the Rebbe is on a higher level than we will ever be. On the other hand, if you are Litvish, you believe that you become closer to Hashem through your own cheshbon hanefesh, sometimes with guidance from a Rav, but that ultimately you are making your own decisions about which chumros to take on (in addition to the minhagim of your family) to help you grow spiritually.
I understand your dilemma because on the one hand you understand the greatness of the Rebbe and want a brocha and advice from someone on such a high madreiga, but on the other hand your being litvish means your not used to the Rebbe’s absolute authority in something that is not strict halacha or minhag (at least not your minhag.) The answer I can give you (and I hope it helps you have more clarity) is actually a litvish way of looking at it, that you have to make a cheshbon hanefesh and decide for yourself if this is a chumra you want to take on, or even to try at all. You asked the Rebbe for advice for a reason, so in your cheshbon hanefesh you might want to decide if there is a different chumra that seems more fitting for you, or if indeed you find after much introspection that shaving your head will benefit your (and your husband’s) ruchnius growth.