Do you like patterned tiles at all? Doesn’t have to be garish and you can keep the pallet simple. I’m thinking tile the whole wall, the same width as the vanity unit, up to the ceiling, similar to first picture. Or if that’s too much, then just tile the space from the sink to the mirror. I would raise the mirror a little so that it doesn’t get too splashed.

They’re fine to use otherwise they wouldn’t be manufactured. However glass is a better material. It will need templating and is more expensive than laminate but is easier to clean. You can choose a BS or RAL number to have the glass sprayed to, but if you leave it clear the colour of the emulsion on the walls will show through so you don’t have to worry in future about respraying it.

Often with upstands people don’t have tiles as it can look a little clunky. They tend to paint the wall above with a washable paint instead. However, if you want tiles how about a pearlised finish, such as Zelig tiles in pink or blue? I can see you like pink!

Shutterstock [website] supply high quality images, either photo's videos, AI images etc and they're sold under licence on behalf of the original artist, so there's a massive library of images to choose from so you should be able to see the image before approval. Then the glass is screen printed on the reverse before going through the toughening process, all the glass i've seen which has been screen printed has looked stunning and i'd assume your glass supplier would have pictures and samples of their work [decent sized not little 100mm squares]. Cost wise though your cheapest option would be as Sonia says to go down the laminate splashback route which is a diy option.