Adding custom "variables" to post

Hi everyone! I’ve been using ghost for a while and I love it. Now, I’m trying to implement a theme myself.

At the moment, I’m trying to make a blog about cooking. For that, I’m making a template for “recipe” pages. Such pages will have some special elements, such as rating (decimal number from 0 to 10) in several categories. To give a very basic and simplified example, a recipe about apple pie would have something like

Calories: 8/10
Taste: 9/10
Difficulty: 6/10

However, I would like to treat those elements in a special way in my template. For example, I could render an amount of sugar cubes proportional to the Calories at the beginning of the post, or use a color from green to red depending on the Difficulty.

While I can do that in the template, how can I add such variables in the editor in a way that I can recall them back when the page is rendered?

The only idea I had so far is to add an HTML card in the post where I define a script container with some variables. However, since the main author of this blog will be my girlfriend who has zero knowledge of coding, I would prefer a more user-friendly and appealing solution. Tagging wont work too as it would require waaaay too many tags.