Bloomers, shorts, leggings

http://www.trendweekly.org/lacey-bloomer-things.html

Does anyone know what these are called?

What sort of body type would they suit best, and are they available in Japanese plus-sizes?

If it helps, I'm a UK size 14-16

The description "furiru reesu shooto pantsu" (frill lace short pants) seems to lead to similar things, though the hem looks a bit different from the one you've got. (The page I've got says "petticoat short pants," but not all shops use this name.) I don't think there is one proper name for this type of garment.

http://item.rakuten.co.jp/auc-glamrich/10000737/