Sharing my BEAKL 15 inspired model 100 layout.
The alpha keys are a BEAKL 15 derivative which moves the h and r letters to the home row on the little fingers.
Layers are accessed via one-shot keys on the outer rows. I find these easiest keys to reach on a flat keyboard.
I’m particularly happy with the symbols layer which was designed with focus on programming.
So glad to see someone else using BEALK-15. 
I’ve been using it for two years now (switched after 20+ years of Dvorak), and absolutely loving it. It is such an underrated layout. I started getting finger pain with Dvorak, and needed a layout that was even more efficient with less finger travel than Dvorak.
I would highly recommend you try the official Symbol layout of BEAKL-15 if you have a chance - it is actually very comfortable to type on. I’m a programmer too. Granted, you might have to tweak your main alpha layout, to not have duplicate keys in both layer.
I’m using BEAKL-15 on both my Keyboardio Atreus & Ergodox. On my Atreus (due to few physical keys), I’m using the home row as dual keys. This was surprisingly comfortable too, and freed up the whole bottom row of my Atreus, for layer switching keys. Long press (>150ms) gives me modifiers, and tap gives me the normal alpha keys. For example:
Left hand Right hand
Tap: Y I E > S T N B
Hold: Cmd Shift Ctrl Alt Alt Ctrl Shift Cmd