Variable post width – can I set up templates?

I’m not particularly tech, but I’m trying – I’m using the Exposito theme and I ALMOST have it how I want it – except for one small, but hugely important thing:

I wonder if anyone has any idea how to vary the content width of a post?

This post, for example, has a long body of text that I would like to make into columns that are the same height as the images (so people don’t have to scroll vertically as well as horizontally).

https://www.gemmarose.com.au/tanja

If I make the standard post wider then the other posts with less content are really far away from the images (see here for a post with less content):

https://www.gemmarose.com.au/red-centre

Is there a way that I can make the content area dependant on the amount of content – I feel fairly comfortable creating columns, just not varying the content width to suit.

Otherwise is is possible that I set up different post templates with various widths – so for example if I wanted a four column post I could choose a different template and make the columns myself?

At the moment I’ve made the post width 400px, and the content 85% of that so there is enough white space between the image and the text, so if I was to make more templates I’m guessing I could make templates that were 800px for two colum text, 1200px for three column text etc…

Thanks, and sorry if I don’t have the right tech terms.
Gemma