I'm on the same boat: a year ago, I bought a first-gen Pixel. Back then, Pixel 2 was already out and even Pixel 3 was on the horizon, but 5" is the absolute maximum size I can comfortably operate using one hand. Hell, I would even take a 4.5" phone with decent specs. My old Moto G was incredibly comfortable.

I held off upgrading from pixel 1 to 3 for ages because I didn't want the phone to be bigger

Turns out that while the screen is bigger, the phone is actually slightly smaller. It just has a longer screen and less bezel

Sony? Their entire existence seems to be around making compacts with flagship specs (even if the latest iteration skips a compact model).

Sony Xperia X Compact here (2016). A little too thick but lightweight. Newer models weigh more.

If it's just about the fact that larger phones generally also have very high dpi (text is too small and hard to read), you can use Android's native dpi scaling to make the phone screen "smaller". I personally can not use newer M-XL size phones on factory settings because the text is too small to read. But then I just scale the display to lower the dpi to a comfortable level in Settings.

This is an important thing to note and I'm not sure designers take it into account often enough. I know I'm guilty of designing an interface that looks good on an iPhone 5s, SE, 6, 6+, and X with default settings, only to watch someone with an 8+ have their scaling turned way up and blow my user interface out of the water.

Alternatively I had an app that worked well on all screen sizes, but one of my friends showed me it wasn't working because they had increased the size of their keyboard and the extra-large keyboard was covering one of the buttons.

Samsung S10e and others from: https://www.gsmarena.com/results.php3?nYearMin=2018&nHeightM...

The S10e is the same size as an iPhone X. Not small at all.

Which is 5.8"? Here's the correct search filter:

https://www.gsmarena.com/results.php3?nYearMin=2018&nThickne...

Exactly. I had high hopes for the sharp r2 compact, which has current high performance specs in a small form factor, but sadly it won't be available in western market. It looks like there is also a demand for small size smartphone on the asian market, so we might see some new ones soon ?

The Pixel 3a is admittedly just outside your size limit, but it's a capable phone at a good price.

Personally I find it right at the limit of a "taller" format phone that while still big-ish, is quite manageable.