I bought my meditation seat online. They have two sizes: small (body height <1,75m): front part height: 173mm / back part height: 195mm large (body height >1,75m): front part height: 213mm / back part height: 235mm
I am 1,90m tall and the large one fits well. I chose the version with the carved bottom, so I can adjust the tilt easily.
I like the brace in the second set of plans, but the L brackets would probably work as well.
"Even if you've read the whole Canon and can remember lots of teachings; even if you can explain them in poignant ways, with lots of people to respect you; even if you build a lot of monastery buildings, or can explain inconstancy, stress, and not-self in the most detailed fashion ... The only thing that serves your own true purpose is release from suffering.
"And you'll be able to gain release from suffering only when you know the one mind."