I really like my current setup, a pair of 24" 4K monitors in combination with my ThinkPad P1's 15.6" 4K internal display.
I don't use an external keyboard or mouse; I prefer the ThinkPad's keyboard and TrackPoint, along with its touchpad for two-finger scrolling.
I run the internal at 300% scaling and the externals at 200%.
One external is directly above the ThinkPad in landscape mode with the left edges aligned. The other is in portrait mode to the left, with the bottom of the monitor an inch above the desk to allow cables to run under it.
Because of my age, my eyes have lost most of their ability to focus at different distances. And sometimes I want to use the ThinkPad on its own. So I use a pair of single vision glasses corrected for the distance to the ThinkPad display, about 20". I highly recommend glasses like these. If you wear progressive lenses (as I do when I'm away from the computer), you will always be craning your neck back so you can look through the bottom of your lenses. This is a recipe for neck and eye strain, and only a small part of any monitor will be in focus at one time. The single vision lenses solve all these problems.
The focus distance also determines where the external monitors go: all three monitors have to be at the same distance from my eyes. The landscape monitor sits where I can open the ThinkPad lid in front of it and have very little gap between them. The top of the ThinkPad bezel is just below the bottom of the external monitor's display area (so the bezels overlap). The portrait monitor on the left is also 20" from my eyes.
All three monitors are angled so the center of the monitor is centered for my eyes: the laptop display is at a typical laptop display angle, the landscape monitor above it is more vertical (but not straight up and down), and the portrait monitor is at a more in-between angle.
At my standing desk, the top of the portrait monitor is just about at eye level, and the top of the landscape monitor slightly below.
Typical use is either Slack or documentation pages on the portrait monitor, or any kind of long form reading. The portrait monitor is also great for PDF files; I can view a full page without scrolling.
Most coding work happens on the landscape 24" monitor. And the ThinkPad's internal display is used for whatever else I need.
I run Windows on the ThinkPad in part because of its better support for different scaling on different monitors. At my work we use Ubuntu for development, so my Ubuntu virtual machine runs full screen on the landscape monitor. I use VMware, not VirtualBox, as VMware has much better display response, almost like running native. And I often run a second Windows VM on the ThinkPad display with the McDonald's Point of Sale system. (I work on a drive-thru voice agent and test it against the POS running in the Windows VM.)
One reason to have the portrait monitor on the left instead of the right is that I can simply turn to the left to read it (turning my whole body, not just my neck) while having easy access to the cursor and PgDn/PgUp keys for scrolling. This doesn't work as well if the monitor is on the right.
I've experimented with many monitor configurations and this has worked out by far the best for me. I tried a 32" monitor when I spent a week at a Google office some years ago, and had trouble with it because the difference in distance for my eyes to the center of the screen vs. the edges was too much. 27" monitors wouldn't work for my setup either: the top of the portrait monitor would be too high, and since the monitors are all 20" from my eyes, I just don't need big monitors. And the smaller size keeps the focus distance more consistent. A curved monitor might help with that, but it wouldn't give me the nice PDF and documentation reading that the portrait monitor provides. And most of the big curved monitors I've seen have rather low DPI compared to these 24" 4K displays.
The two external monitors are mounted on AmazonBasics monitor arms. These are actually made by Ergotron and are identical to the ones Ergotron sells under their own name, but the AmazonBasics arms have a matte black finish instead of the silver of the Ergotrons. I like the black finish because it is less obtrusive visually.