When I was not self-employed my company forced us to use an external monitor, keyboard, mouse and a chair with armrests, because of regulations. I bet those regulations are there for a good reason but after 16 years of self-employed working from home on my laptop (no external monitor) on a 5 wheels chair with no armrest I'm still fine. I definitely prefer looking down than up. It's easier on my neck and I can look both at the screen and at my hands and touchpad. Not that I need it but it probably helps somewhat.

I removed armrests because my wrists are resting at the side of the touchpad. I never touched the armrest unless I was standing up or sitting down.

The only way I could go laptop-exclusive is with a VESA mount laptop stand attached to an adjustable monitor arm. I've grown too used to my desktop monitors sitting at the perfect height thanks to the arms they're attached to.

I think I'd be quickly frustrated though because even on a 16" MBP, using an IDE like Xcode or Android Studio the screen gets jam-packed so easily with all the panes and inspectors and such. That screen size is probably like a football field to the vim/emacs types though.

I use a Roost laptop stand with a keyboard and mouse. Works great.

https://www.therooststand.com/

I do put it on a stand and use a Magic Keyboard and trackpad.