The walnut would look nice. it's an option. just depends how much you want to spend, and if that quartz piece can be removed w/o cracking.

you could look into a pre-fab island piece. they usually come in 3x5 or 4x6 finished edge slabs. I've used it on a house we did. cost for that piece was only 400 or so. then whatever your fabricator charges to install it. Even using a remnant for that island is an option. if you can find a half slab piece, it may work. Either way, shouldn't cost more than 1K. (depending where you live. out here in so cal that's the cost)

see about doing a waterfall (yes more money, but very nice looking)

Finding a nice walnut slab for that island would be as much as pre fab or remnant stone piece.

btw, do you have plans for a backsplash? it would really take up your space a notch if you did something.

Just think of it as a table, you want

to add. Not with legs(they probably used something heavier than wood for the tabletop) & Don't get stuck on the granite vs white top, it will look fine to have a carpenter create a table top 'shelf'. Make it about 15 inches deep If that works in your space..I have seen some that are 9 inches deep...that's a bit narrow.... Paint it like your cabinets are, white.... You can support with 3 wooden braces that are also painted white, beneath it. It can have a blunt edge piece on it probably 1.5 inches down to make it look finished...Braces, painted white also, They would be shaped like in inverted L, or if you wanted fancy, you might find something in wrought iron, but why spend the money?? Go ahead and make it table height because those chairs are much more affordable!!!! and they sit better. You probably can sit 3 or 4 chairs there? You will enjoy it for years to come! And it will not break your budget. There are many ways to do this. I just think if you blend it into your cabinets you will be more happy with it. I hope you like this idea? :D

if you add on... don't go 'full meal depth', or you really will be running into your table. one can perch with just 8 inches or so of counter.

If there's room, I think a wooden top with some overhang for the island would be perfect! It would bridge the wood tones in the eating area and also nod to the floors. While not exact, the concept is illustrated below.

Charlestown Beach Cottage · More Info

I wouldn't skimp on the overhang depth. Even if you do, the stools stick out.

What is the distance from the island to the wall of the dining area? And what is the width of the table?

You might just do something like this that is a 12" deep bar height table that spans the island. It's not the most civilized, I guess, but 42" is comfortable standing-to-eat height. And then your not dealing with the clashing of dining chairs and counter height stools.