Low fire Porcelains are just as easy as hi-fire. The difference is that they incorporate a Frit instead of feldspar to control the degree of maturity. My cone 04 recipe using Dragonite kaolin requires 30% frit 3110. For regular cone six Porcelains. 30 to 35% feldspar is needed for it to be vitreous. For cone 10, 20 to 25% feldspar.
All of them need from 20 to 30% silica. Higher silica amounts are required if glazes craze.
The remainder of the recipe is Clay. The whiter and more translucent you want the more expensive clay you use. White Porcelains typically only use kaolin, no ball Clay.
Given the constraints mentioned, the Clay percentage will be from 40 to 50%. The last factor to consider is plasticity. You achieve that by adding the whitest plasticizer you can afford. Veegum he is the most expensive, and the highest practical percentage is 4%.
By firing it and checking the surface character, tendency to warp and the degree of translucency you know whether you have enough or too much feldspar.
By noting crazing you know whether you have enough silica.
By noting its workability, you know whether you have enough plasticizer. Or too much if it is cracking on drying.
Here is a page about formulating a Porcelain:
https://digitalfire.com/article/formulating+a+porcelain
The process is not so much about wondering about the mystery of the recipe. It’s more about being willing to weigh up small batches like 2000 g, mix them in a blender and pour them on a plaster bat to dewater and use them. It’s about code numbering each and keeping good records. If you do that half a dozen times, you will end up with a Porcelain that is not perfect, because that’s impossible, but you will end up with one that you understand and that you have adapted to your situation.
I would start with the recipe we already talked about. As I remember it was 30% feldspar or nepheline, 30% silica and the rest is kaolin. And then add the amount of plasticizer needed.
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