Building handcycle hometrainer

Hello everyone!

I start building handcycle hometrainer.

At the start, the project uses old bikeframe and massmarket plastic seat. It looks like this: Youtube, @boristsybin, Handbike hometrainer v0.1 First test. (sad, cant include direct links in posts)

Now im looking for ideas and techs to build custom, preferrebly amatomic, seat. Googling lead me to this video: Youtube, @ThinkingandTinkering, 1179 How To Make A Recumbant Bike / Trike Seat

So, is there any realy easy way to get shape of my own back, or any “average” curve shape with exact dimensions i can use to build seat.

Or, may be, flat seat is enough?

Thanks for any answer.

p.s. Wonder why Zwift (Wahoo or Tacx or whoever) still NOT build some kind of home handcycle kit.