I would attach it to the vanity, it is awkward to try and reach behind you if you attach it to the wall or you could try a freestanding one that you could put anywhere though they might take up a bit of room when space is a bit tight

En-suite layout is fine, Looks like you have a double hung window with a slightly lower sill to the vanity height. . I’d put a stool in front next to shower screen. Update vanity and top and splash back, maybe lowering mirror. Could put a niche in the side wall if want extra storage. Could change mirror to a cabinet, even if it protrudes, mine does, A smaller basin would increase spaciousness and bench space. Can also increase depth of vanity, to 550. Replace floor tiles if you want but I’d leave shower if you want to keep costs down. otherwise retile to full wall height will improve look. Could add a pendant light over left side of vanity

Hi, I would recommend asking the company where you purchased the vanity from what there Warranty period is?

the top of a vanity could be 780 (approx desk or table top height is around 750) or as high as 900 which is average kitchen cabinet height but is it for tall people, short people or average sized people and, as the space under the vanity is not tall enough for anything but dust and lost pills why not make sure the tops of the sinks is no higher than 900 for comfortable height for most people and that would make the floor space 220, the counter top 760 and the top of the basins 900?