I do love my 2018 12.9". I will admit that for mobile use, on the lap, I do struggle a little using the Apple cover/Apple Keyboard. Maybe it is my physical build, but the iPad tends to slide down my not perfectly level lap. Maybe I should work out 
But, I'd hesitate to go much smaller as I enjoy the multiple screens. To be fair my eyesight requires a bigger iPad screen as I struggle with some of the smaller fonts. So the 12.9" fits that bill.
For home use on the couch I found this to be fantastic! The pad, and the various angles work well. You can also put the iPad in portrait which I've found useful for reading long articles. Scroll less read more
It isn't really all that portable, as the bottom padding adds to the thickness of the stand. Though the holder does fold flat. So I can't recommend it for on the go.
For desktop or table use I use the Apple folio/keyboard or the Twelve South Compass Pro portable stand.
www.twelvesouth.com
Heck, sometimes I wonder if I'd be better off with a second and smaller iPad for mobile, or a MacBook Air. But I'm so used to iPad OS I'm pretty happy to make adjustments to use the 12.9" 2018.
To each his own I guess. It is good to read these forums and learn what works for other people and adapt their ideas.
But, I'd hesitate to go much smaller as I enjoy the multiple screens. To be fair my eyesight requires a bigger iPad screen as I struggle with some of the smaller fonts. So the 12.9" fits that bill.
For home use on the couch I found this to be fantastic! The pad, and the various angles work well. You can also put the iPad in portrait which I've found useful for reading long articles. Scroll less read more

Prop 'n Go Slim - Adjustable Bed Holder & Lap Stand for iPad, iPad Mini, Tablets and eReaders with Multi Angle Control (Striped)
Tired of leaning your against coffee cups, stacks of books, or piles of pillows to find a good angle?
www.amazon.com
It isn't really all that portable, as the bottom padding adds to the thickness of the stand. Though the holder does fold flat. So I can't recommend it for on the go.
For desktop or table use I use the Apple folio/keyboard or the Twelve South Compass Pro portable stand.

Compass Pro for iPad Pro from Twelve South
iPad Pro's ideal companion: Compass Pro – versatile metal stand for 3 viewing angles: hands-free, interactive, or typing/sketching. Now with SideCar for Mac.

Heck, sometimes I wonder if I'd be better off with a second and smaller iPad for mobile, or a MacBook Air. But I'm so used to iPad OS I'm pretty happy to make adjustments to use the 12.9" 2018.
To each his own I guess. It is good to read these forums and learn what works for other people and adapt their ideas.
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