Hi analog 999,
I learned something with our dinette shown. Maybe you can take something from this.
When ordering our rig new in 2007, we saved money by getting the standard foam cushions and the cloth coverings shown. This was "extremely" uncomfortable. The foam did not support well at all and the cloth was like glue. We had to lift our rumps and shift in the air to get out and even just to do simple repositioning on the seat.
It was so bad that a few years later, I ordered the upgraded cushions that are made of a very dense foam and vinyl coverings. They offer a HUGE improvement in comfort. The dense foam was much more supportive (no sinking in) and the vinyl allowed us to easily slide in and out of the dinette. I am able to shift my body weight, turn a bit here and there without a fret. The bonus to the more dense cushion is that it is slightly smaller than the original cushions, making for a more roomy dinette.
So keep this in-mind when building a dinette. If not careful, you could have serious regrets. I advise to keep the cushions simple like we have, and made of a thinner and very dense foam for maximum support (easy to shift your weight and easy entry & exit) and also getting extra elbow room.
For us, the change was very dramatic. We went from hating our dinette to loving our dinette.