Measure the sinks you have. Are they too big, too small or just right?

Or go to a local good plumbing showroom and they will have several sinks on display that you can view in person.

I like the Kohler Ladena undermount with a cutout of 18x12 inches. It will fit easily on a 24-inch deep vanity. Toto makes a similar size rectangular sink.

The code for spacing the sinks is as follows: Minimum recommended distance from the centerline of a sink to a wall is 15 inches; however, the NKBA guideline recommends a minimum distance of 20 inches. The minimum distance between the centerlines of two sinks should be at least 30 inches (IPC 405.3.1), but 36 inches is recommended.