Get thongs/G strings.

or dont wear any.

You can wear a petticoat underneath. It's a thin beige/white/black dress. Prevents the lines of underwear showing.

seamless ones haven't come up? I'm sure they are available at your local lingerie outlets.

example: http://www.myskins.com/panties/

There's an item called C-clip. Easy to use, just attach on the private part and it doesn't have/show the panty line. u may find it in local lingerie outlets.

Can try to buy online.

try Spanx

petticoat (or half-slips) will only make a slight difference because it doesn't actually flatten the contour like how a pantyhose would. They serve more of a purpose of not having your skirt cling onto your skin when you sit and stand.

But you can get very nice nylon half-slips/petticoats at Jusco, Scarlet halfslips are like RM10 each.