Out of all the ones you’ve listed I like the one from Perch and Parrow but I’m confused when you say footprint within 48x48cm and this one is listed as 42x42cm. Incidentally I found them cheaper here: https://www.costco.co.uk/Furniture-Home/Dining-Room-Furniture/Chairs-Bar-Stools/Gallery-Palmer-Brown-Faux-Leather-Bar-Stool-2-Pack/p/263151 Also found this one: https://www.wayfair.co.uk/furniture/pdp/selsey-living-hoker-65cm-bar-stool-tcdv2652.html?piid= And a bit of a wild card but the cantilever might make it extra comfy: https://www.argos.co.uk/product/8835576 Also have a browse in the Houzz shop. They have lots of barstools so you may find something there.

Depending on what colour your kitchen hardware is, there a couple of options that would work well in a graphite kitchen. If you have white worktops and a grey kitchen, I would add another colour or texture to the stools to create another layer to the scheme. If you don't like using bold colours, you could use an interesting textured metal or wood for the stools. You could try using something similar to the silver wire stools below for a more industrial style Or wooden stools are always lovely for a more contemporary country look. I would use a lighter wood, to add contrast to the dark grey kitchen and white worktop All the best with your project

The swivel ones usually have a lever that activates the gas that allows it to go up and down. The gas mechanism is usually within the middle pole. That way you can adjust the height. I have seen some that adjust the height by swivelling round, swivel one way the seat goes up and swivel the other way it goes down.