Change 700c rim to 650c
Changing to a smaller wheel may cause other problems, such as needing brakes with a longer reach (that won't work as well), or the bottom bracket is lowered, so the pedals may ground around corners.
This bike is super small already - the fundamental problem is, as you have guessed, the wheel size, which governs the dimensions of the frame.
I would be looking at a bike with 26&quot; wheels, or even 24&quot; - they generally didn't make road bikes with these wheels, so you might need to adapt a mountain bike or a kids bike. It is quite possible to put road bars and gears on these frames.