the normalized version of this model would store the width and height measurements separately and your print_size text would be a presentation issue.
I second this approach as it should be normalized into two fields. It would then be a simple order by area.
i.e. order by width * height
This would work in the meantime, given the data format doesn’t change:
order by split_part(print_size, 'x', 1)::int * split_part(print_size, 'x', 2)::int
