Don't do the lower back!
Bullseye, tramp-stamp... either way; not the best place for a tattoo.
You say it's going to be small. How small? I would tend to suggest the flag over the boot, because the boot will lose detail the smaller you make it. Also, each person's body takes different inks in different ways, but I believe white is one of the more difficult colors to tattoo.
For location, I'm not a fan of ankle tattoos either (look trashy IMO).
My vote's for the pelvic area or upper back.