First off, take a look at the
Keyboard Discussion thread to get a list of options you might find useful. I'm not familiar with ISO specifically, but let's take a look at other things you mentioned.
1.) You said 'slim design.' To me, that says one of 2 things, or a combo. - a low-profile keyboard (thinner) or a more compact keyboard that gives up some keys to make it narrower horizontally and sometimes vertically (e.g.: a 75% keyboard, or even 60%).
2.) Wireless connection. There are 2 forms; Bluetooth and via a 2.4 GHz receiver. Often the latter is referred to as 'wireless,' even though Bluetooth is also a wireless technology. And with the 2.4 GHz receiver, you might pay attention to polling rate if you're into gaming.
A big question you need to decide on is membrane vs. mechanical, and if mechanical (a big rabbit hole to go down), do you want hot swappable switches and if so which?
That Nuphy Air75 V3
@xraydoc mentioned has been getting attention; Cameron Dougherty Tech has a video review on YouTube about it:
NuPhy Air75 V3 Review: The Next Evolution of Low-Profile Keyboards
I really like the look of Apple’s official keyboards and the feel of the keystrokes.
I'm guessing you're talking about their membrane keyboards. Question...do you need this keyboard to operate only via Bluetooth for wireless connection, and only with one device?
If you want, oh, say, the keyboard to have 3 buttons you can hit to switch between 3 devices (e.g.: Mac, iPad, something else), then you're not buying Apple. On the other hand, if you want a touch I.D. finger print function on a keyboard, I understand Apple has a keyboard with that.
