Sometimes great art translates poorly into tattooing. You have heard your options. Bigger, or less detail, or softening of the sharpness over time. A single needle done with a sure hand can execute some very fine, sharp lines indeed. Modern black pigments are much less prone to fading and bluing over time, but ink is still going to spread and settle in over the years. Getting the fineline work refreshed would not be that bad if you ask me. I have fineline work twenty years old that still has sharp, clean edges even though the ink is blued.
I would shoot for a 5×7 size at a minimum.

And choose your artist carefully.