A group is always more harmonious when characters are proportional, true, but you also have to think of your feet. You didn't mention how high the boots were...
My suggestion, get some boots with a chunky heel and a platform, they won't hurt your feet as much as thin high heels and you will be a lot more stable on them.
By experience, I would say to stay under or equal to 4 inches. Anything else will strain your back and make you really uncomfortable.
Maybe you can make sure the others wear flats, and just wear a 2 inch heel? 2 inch heels will give you a little more height, and are ultra-comfy.
Moreover, you can always cheat for the pictures.
Have the one out of proportion sitting, kneeling, or bending down. Or have the tallest ones stand with their hips out to one side (you know the usual "sexy anime" pose), while you stand extra-straight, this will make them look shorter.