the one in Dudgeon's pic is especially good because there is no wooden or laminated worktop that water will find its way into, and fall apart. The basin and worktop are all in one piece. Preferable ceramic, plastic ones are available but flimsy.
Please don't put a shelf or cupboard on the wall above it, as a glass bottle or jar will fall out and crack the basin. Just have a mirror.
The curved front looks as if it is cut into the cabinet front, but in fact they are usually made so they fit onto an uncut cabinet.
I prefer the ones with big roll-out drawers to the ones with cupboard doors, you are less likely to lose things at the back of shelves. The top space will be full of pipes.
The units are available in numerous widths, IIRC 1200, 1000, 900, 800, 600 and possibly 500 or 400mm (for cloakrooms).
It is always a bit of a risk having a cabinet made of chipboard or MDF in a bathroom, as they react badly to damp.