I love that you re thinking of full backsplash.
Vessel sink backsplash height.
We do this all the time for multiple reasons.
Standard back splash on a bathroom vanity is 4.
The height to the top of the vessel shoud be 35 plus or minus 1 inch.
A 4 deep vessel should be on a 31 vanity.
Pick a vanity that supports the sink at a comfortable height about 36 inches to the top of the bowl is typical.
Also use a tall faucet with a long spout designed for vessel sinks.
Vessel sinks to attain the ideal height for your vessel sink and vanity add the height of the sink to the height of the vanity and adjust the vanity to fit the desired height.
What is the standard height of a kitchen sink from the floor to the top.
Taller vanities will work but keep in mind that children might have a hard time reaching over the sink bowl.
An above counter vessel sink will naturally sit much higher than an inset below counter sink and so a vessel should be placed on a lowered cabinet to compensate.
Ultimately you should try a few different sinks and figure out the height that feels most comfortable for you.
Work with a bathroom designer on houzz.
If you leave it at the 18 behind the sink it will look unfinished whereas going all the way up will not be that much more expensive but will create flow.
Since you have a vessel sink and i know are thinking of splash protection you can go higher or another option is recessing the sink into the counter a little.