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.
"When you meditate, don't send your mind outside. Whatever knowledge you've gained from books or teachers, don't bring it in to complicate things. Cut away all preoccupations, and then as you meditate let all your knowledge come from what's going on in the mind. When the mind is quiet, you'll know it for yourself. But you have to keep meditating a lot. When the time comes for things to develop, they'll develop on their own. Whatever you know, have it come from your own mind.http://www.accesstoinsight.org/lib/thai/dune/giftsheleft.html"