I prefer fully split keyboards overall, but every time I go back to using my Atreus I'm reminded what a nice keyboard it is, and how lovely it feels to type on it. Those guys know what they're doing.
Just keep at it. I took me a couple weeks and then I was at the point where I could easily switch back and forth. But I had the same thing where after the first few weeks of using ortho, I had some issues going back. But they went away pretty quickly. For a little while I kept trying to switch back and forth each day, but not sure if that helped. These days I'm mostly moonlander, but when I'm traveling or on a plane, I may just us the laptop and my brain/fingers just know what to do.
So, basically, keep at it and you'll be fine.
This was also my concern. When I first got an ortho, I spent 3 days 30 minutes each training how to use the ortho and then it just clicked. Then, I used only ortho for a couple days, then went back and forth between ortho and staggered for a few days. And... now I can switch back and forth with ease. It's surprisingly natural. There is a slight learning curve at first, and then it's easy.
I recently picked up these, and they've been perfect. https://www.amazon.com/dp/B08ZY2WFHX
Yeah, I get it. I say the same thing about boards with no number keys and people tell me I can just use layers. But for whatever reason, layers for function keys makes more sense to me. It's just like pressing "shift" except instead of "shift" you press a different button and the number/function key.
I know of almost no ergo boards that have dedicated function keys. Moonlander does have number keys though... and you can use layers to turn those into function keys...
I have a Moonlander and find it works well for me. Took a little while to get used to, but really not long, and the longer I used it, the more I liked it. Not sure what you mean that it doesn't have many keys, as it has way more than a lot of ergo keyboards?
Gateron low profile switches... which seem (slightly) better than chocs for low profile switches. Also, I think that the Gateron low profile switches work fine in MX hotswap sockets.
Not only do they, they're relatively inexpensive (compared to some other keycap offerings...) and they seem to have sales every so often too.
Keycaps are from Nuphy. Using Gateron low-pro switches, which I think are compatible with standard Cherry MX switches...