I have no idea what SIRM's position on the biopsy is as I wasn't a patient there, but I had the opposite issue - 2 normal uterine NK biopsies over several years but sky high NKs at times, particularly with implantation & during my 1st pg. (But not my 2nd pg.)
It may be worth getting a couple of opinions, futurebeauty. It's a pain but navigating the information on this subject & trying to make the best decision for yourself is usually not easy. Unfortunately. Doctors even within the field vary somewhat on testing & treatment, so you have to educate yourself in order to know what questions to ask & how to evaluate what you're being told.
If you haven't already, may I suggest you get Alan Beer's "Is Your Body Baby Friendly?" It will give you a lot of information which will help you evaluate issues, treatment, etc. It's just a really good starting place. See if any of it resonates with you.