Pixel 7a is the absolute biggest I can semi-comfortably type one-handed on. I can’t imagine why bigger ones are more popular - don’t people ever use their phone while on a bus and holding onto a handle?? I guess you could use a “one-handed mode” on the keyboard, but I never use it because it makes the keys waaay too small.
When I was buying mine, 9s weren’t out yet - even now, the 8s are around $400 where I bought, while 7s are at an already crazy $300.
I didn’t get the impression that the plastic was easily breakable - seems relatively soft. While the base and pro have glass.