tbh i love the look that you have now. but If you go white, I always recommend some movement. Seaming all white can be difficult and will leave you with a more prominent seam than you would like.

https://www.msistone.com/quartz-countertops/calacatta-luccia-quartz/

https://www.msistone.com/quartz-countertops/portico-cream-quartz/ 

That stainless backsplash has a lot going on in both shine and texture. I'd avoid a quartz counter with a pattern and think your instinct toward a plain white, or plain gray, counter is a good one.

You've got quite enough sparkle already. No sparkle in the countertop.

If you want a plain white countertop (which would look very nice), do Corian in Glacier White. It will appear completely seamless, it will wear like iron, and it will be easy to keep. If you're set on quartz, use a Carrera look-alike that is plain and has as little movement as possible.

There might be some damage to your back splash when removing old counters and installing new. Hope you have some extra tiles for any needed repairs.

MSI Calcutta Vincenza or Silestone Lyra

This is the Lyra

silestone lyra countertop · More Info

Calcutta Vincenza

Prairie Village Kitchen Shaker Style · More Info

A simpler countertop will let the back splash be the hero and lighten up the space.

Another vote for Glacier White Corian. Your backsplash is quite beautiful. Let it shine.

For me, I chose Corian because it's warm to lean against whereas granite and quartz are cold. I don't like that. I love the Corian, never scratches, easy to clean, doesn't require polishing and isn't SHINY! I have these, gorgeous. Gorgeous Corian

Heating mats under stone are common for install so they "are not cold". Stones can be honed so they are not shiny. and most natural stones are hard to scratch and easy to clean. Natural stones will help resale value over Corian or formica

I love what you have, but then I've never liked white countertops. I would reserve Corian for the bathroom - it looks cheap to me. Of the white choices, I think marble looks the best - I really do not like the white quartz that I've seen so far, but quartz is what I chose for my own kitchen - but it is primarily black.