Take a piece of non-stretchy string and encircle your ankle snugly (but not tightly). Measure the string, then add about a 1/2 inch. This will give you a pretty good size estimate for an anklet that falls below the ankle bone.
Gold-filled is the closest alternative to solid gold. Gold filled jewelry has a thick layer of solid gold bonded onto the base layer, usually brass or sterling silver. Compared to gold plated which uses a process of electroplating that quickly dips your jewelry in gold, resulting in a miniscule layer of gold, gold-filled is much more durable and long lasting. Feel free to live your every day life in these pieces and feel confident in the quality!