I have been wondering whether a Onewheel (https://onewheel.com/) type of a board would do in bumpy meadow?
Not good. If off road, a onewheel needs smoother ground than a mountain/land board.
With bindings/straps on a land board, you can unweight the front foot AND lift the board by pulling up on the strap to get over a large bump. Whereas all of your weight is always concentrated on that "one" wheel of a onewheel at all times.
I kite with a mtn board frequently in a field with lots of small humps and bumps, tall grass etc.
I went from 8in to 9in wheels and that helped.
Also, being really powered up with a relatively big kite makes a big difference. (But be careful if you haven't tried it before!)
The upward vector of the kite reduces your effective weight on the wheels as they pass over bumps. You're pulled up and over the obstacles. In contrast, my hand-wing doesn't work at all with mtn board in this field because the force it applies it mostly sideways. The added benefit of being powered up is that boosting is easy.
Riding mtn board improves your kite skills a ton and is so much fun.
I went through this phase as well. Tried the 9" tires, but they didn't solve the problem. Use Google Earth to locate potential fields then go scout them. Soccer fields and parks are great in the off season...if you can find ones you're allowed on.
Ultimately, I ended up selling my landboard and investing in a really good drysuit and a bunch of cold water undergarments (Helly Hansen makes great stuff) as well as a battery powered heated vest.