I used to set userdata for text objects reflecting relative font size. Then when I got a figure resize callback, I would figure out the base size and findobj() to get the text objects with the special marks and use the information there to modify the computed base font size.
I used this approach instead of a plain set(findobj('type', 'text'), 'fontsize', X) in order to allow for headers (larger than normal) and explanatory text (smaller)
Though really what I did was use this marking process along with a user font size preference, changing all the objects when the user modified their preferences. I also implemented dynamic uisizing and text wrapping so that as the user made the text larger the boxes did not overflow. The logical also auto positioned controls according to a system of layout rules.
... Basically my boss used a different sized monitor with different sized pixels and configuring against their monitor would have had the interface look crappy for everyone else, so I did autolayout to make everyone happy.
Autolayout is harder to make look good than you might think!
