Going bold is one option, however i see a  very restfull, clean design. My thoughts immediately went towards continuing with that feel with a tile with only a soft hint of color, a tile with an uneven surface to create movement, or a tile with  'mother of pearl' finish on a soft white to be all color yet none.Your indoor plants will bring live color and not be overwhelmed on busy counter.

Again it depends on the look you're going for and it's difficult to advise without samples of the kitchen unit and floor materials. Always plan the room as a whole rather than looking at elements in isolation. That said, a good dependable choice would be a satin white brick or square tile. You already have quite a trad kitchen so I would go for something a little more contemporary and steer clear of anything with a bevel. The balance between pale grey units, darker grey countertop (plain) and fresh white tiles should work well, particularly if you can find somewhere for some open shelving in a light wood tone to balance the floor. I've attached an image of a kitchen I refurbished in an Edwardian house I subsequently let - excuse the quality of the picture, it was for my info only not for marketing but it gives you an idea of how satin white tiles can work against a stronger neutral, greys and wood tones. That was a mix of two F&B shades but something like F&B Ammonite, Cornforth White or Purbeck Stone or FE Bone White would work with flooring, tiles and units. This is just a steer. It really is essential to do sample boards and look at how the shades work together. Keep the paint shade unsaturated and steer clear of DIY paints. The branded paints are much richer recipes. If the budget will stretch to it, get some accent lighting in - lighting is often neglected but can make or break a scheme.

Thanks to bad renovation timing coinciding with the start of Covid lockdowns, we used DIY removable wallpaper above our upstand as a temporary “make do” measure because all work and shopping had to stop. Three years later (!) we are finally getting around to removing a chimney breast to completely finalise the kitchen, including replastering, and I am fairly certain I will be using the same wallpaper again. The only difference is it will be professionally hung! We have received so many compliments and it’s been shockingly robust, even behind the hob. We used a greyish shiplap patterned wallpaper above a Carrera marble countertop and upstand, with white upper and pale grey lower cabinets.

With real timber worktops I'd recommend an upstand as there should be an expansion gap at the back [also where the worktop is screwed down to the base cabinets, slip brackets should be used], then tile on top of the upstand, might have to raise the sockets though as they look a bit low tbh.