I actually asked in /r/MechanicalKeyboards, but they didn't help much, just pointed me to Unicomp but that's not what I'm looking for as it's basically the same size as the Model M. It looks like Unicomp will be releasing a "Spacesaver" Tenkeyless model in the upcoming weeks [1], that might be an option.
The Filco Majestouch 2 Ninja TKL [2] is one of my top candidates right now, or a Ducky One 2 TKL [3] variation. I actually tried to get both in the past weeks: the Filco couldn't get shipped because of COVID-19; and the Ducky One 2 ran out of stock (the European market problem I was mentioning before). Very frustrating.
About ergonomic keyboards I don't want to go through the pain of relearning how to type. I have been typing on the Model M for 25 years now and my muscle memory is deeply engrained, I want a layout that is as similar as possible (so 80% Tenkeyless).
The Planck seems unnecessarily small to me. I'm not moving my keyboard so the absolute smallest size is not a requirement, I just want to get rid of the numpad to have the mouse closer.
[1] https://www.reddit.com/r/MechanicalKeyboards/comments/frr2xh...
[2] https://www.keyboardco.com/keyboard/usa-filco-ninja-majestou...
[3] https://www.duckychannel.com.tw/en/Ducky-One2-Skyline-TKL or https://www.duckychannel.com.tw/en/Ducky-One2-White-LED-TKL