Dainey,

You will have to have a solid surface or natural stone top with an undermount sink. You can special order a solid surface top with integral bowl from Leslie Marble, thru Lowes. That would be the most economical solution. You can get natural stone tops with many different style sinks, but the 18" dimension limits you. I would go to one of the big box stores and look at all your choices.

Hope that helps,

Dan

ikea bathrooms has both counters and sinks these sizes.

there are some undermount sinks that are 12x15 or so; we put one in last week. You should be able to search online or go to your local big box hardware store and flip through their catalogs.