Seats - Principles for comfort
are there any resources I can use to find design principles for comfortable seating?


Here are a few to get started:

Must-Have Measurements for Comfortable Seating


With a little work the drawing above can be turned into an algorithm.
The key variable will be the dimensions of the person sitting in the chair.

Another useful drawing:

I found the picture here but I don't think this is the original source. 

From Concept to Comfort: Build a Casual Chair
Good article describing the process from ideation to finished product.  

Summarizing:
 1. Ideation
 2. Sketches
 3. Prototyping
 4. Testing
 5. Adjusting (iterate steps 3, 4, and 5 until happy)
 6. Build final version  

The steps are not unique to chair creation. This process should allow you to build experience, gather data, and derive the information you seek.

Other resources:
Standard Dimensions for Furniture Design