I don't know of any board that cover 100% of your requirements. I've never looked much into the 34 keys keyboards.
The Piantor is close, but it's wired and 36 keys.
The Totem is 38 keys and adds splay. Might be worth considering though. Here's mine:
You didn't explain how you have your Colemak layout setup but I think I understand the problem. I just tried adding Greek to my computer (Corne keyboard, Colemak DH) and it worked as expected.
Can I suggest you try this:
This way, the computer doesn't even know that you are using Colemak. And it works with all (or most of) the languages!
Miryoku is worth looking at for layout ideas. But using it as-is of a non starter for me.
I'm still slowly making changes to my layout. It has some features that you say you don't like in your blog (numpad on the left) but it works for me.
I thought I needed the aggressive stagger... until I tried it.
I'm in Europe so the shipping to the US would be expensive. Anyway I'm not sure I want to entirely give up on it.
It is the wireless ZMK version, hotswappable switches, resin printed case. It is very nice.
Thanks. I'm used to my own config. https://github.com/y-muller/zmk-config-public I have the missing switches on the keys I use the least, but on some layers I do need them.
A while ago, I bought a pre-built Totem and just enough switches. I could never get used to the large stagger and the splay.
When I saw a relatively cheap wireless Corne on Aliexpress, I thought I'd have another try at a low profile keyboard. I didn't think of checking how many switches I had. Well, I'm two short! Damn.
Otherwise, the keeb uses ZMK and it took me a minute to flash it with my config.
A lot of combos, basically.
There is an example of config in the keyboard's repo. https://github.com/kilipan/teenspirit
Very nice boards. I don't think I will ever go to such a low key count.
My main keeb is a Corne with a couple of keys rarely used. So I'm going to give 38 keys a try with a Totem. I think I can deal with 4 keys less but there is also the increased pinky stagger, splay, smaller Choc footprint, flatter keycap profile. Let's see...
Here's a list of vendors. https://wiki.keyboard.gay/VENDORS.html#continental-europe I've used Delta Keys, Oblotsky and 42Keebs. All good.
Edit: another list https://kbd.news/vendors/Europe
https://github.com/y-muller/personal_configs/tree/main/xkb My notes about customising the keyboard in Wayland. It's brief but should get you started. And if you look around the repo, you might find a few other ideas. ;)
I keep my keycaps blank. It's simpler that way. I made pictures, as above, to help at first.
Keychron ships from China even if you order on a site in Europe. But it is quick and all charges are already included. I like their keyboards. The V series is very nice for the price.
With the large number of languages you are working with, I think it is worth spending a bit of time creating your own layout. The AltGr layer is where you'll want most of your changes.
On Wayland this is not too difficult to do. On X11, skip the headache and modify the system file.
This is my current Alt layer, mostly for French, with Spanish also being easy enough. My main layer is mostly UK/US alphas. This is on a split 42 keys keyboard but the concept is the same.
If there are some characters that you use very rarely, don't forget you can probably get them with a Compose sequence. For example, I forgot the ß when I redesigned the layer, but I can still get it with Compose + s + s.
I previously switched from ISO to ANSI and it doesn't change much. If you make your own layout it doesn't matter. I think you have an extra key in ISO.
Keycaps? I use blanks. But there are a lot of EU vendors. I can point to a few later.___
But if you meant the thumb keys should angle down, then I think your only option is to design it yourself with the help of one of the online tools for Dactyl type keyboards.
I am not convinced those are a good ergonomic design however. The thumbs are much stronger for a sideways movement. Like playing the bass guitar.