My situation was somewhat different, but the two main options that I know of are an office biopsy and a "hysteroscopic D&C," which is done in the hospital under anesthesia. I had both of these, or rather, I had a failed attempt at an office biopsy, and then a month later had a D&C. From reading this forum, it sounds like failed office biopsies are quite common. It should be somewhat comparable to a pap smear, except that they have to push the little plastic stick through the cervix. Not being able to get through the cervix seems to be the cause of failures. I learned on this forum that some doctors have women put misoprostol pills in their vagina prior to the office biopsy to soften the cervix, which apparently reduces the failure rate.

My 2 cents worth is that you should definitely at least have a biopsy: you don't just have slight endometrial thickening, you have symptoms too. If a D&C is possible with your vaginal narrowing, it might also make sense to go straight to that, in the hope that they might scrape out whatever is causing your problems, even if it is "benign."