Maybe not quite what you're asking for, but there are special chainrings that can convert that 144mm BCD double crank into a triple crank with a 74mm inner BCD. Although a 74mm BCD can fit a inner chainring as small as 24 tooth, for best front shifting performance you'd probably want an inner chainring more like 32 teeth.
Here's one of the special "triplizer" chainrings from Red Clover:
https://www.redclovercomponents.com/..._42_Teeth.html
You'd likely also need a new front derailleur to handle a triple, but judging by the current derailleur you have friction shifters, which would work just fine with a triple front derailleur.