How can I transform a single vanity sink into a double sink?

The first thing is to make sure that you have the room. Usually at least 60" is required for a useful double vanity. Then plumbing needs to adjusted, a large cabinet that will hold two sinks is needed, new countertop is needed and then two sinks need to be installed.

Integrated sinks (first picture below) are the easiest to clean, as the basin is molded out of the single piece of countertop. There is no additional 'installation of the sink' required, and no seams or joins with this style.

Undermounted (second picture below) sinks take less counter space than overmounted (third picture below) sinks for the same inside basin size, but they are most easily installed in a solid surface countertop, which is more expensive than laminate. Faucets are usually mounted on top of the rim on an overmount style.

Vessel sinks (fourth picture below) are often recommended if the inside vanity or cabinet space is limited. Vessel sinks require a taller faucet or taps. If the countertop is shallow, sometimes the faucet can be mounted on the wall to conserve space.

Are you wanting to keep the present sink, and purchase another one, or go with two brand new sinks the same style?

Not enough space for two sinks

You have to replace top , add additional plumbing and need at least 60 inches.

You'll need enough space, here are some instructions: https://www.youtube.com/watch?v=M1d_puqCq3A

Thank you so much!

Did you ever change out your single vanity for a double?

Just curious to see and know jow it went.