Why felt suits portraits
Needle felting is forgiving in the way photography is not. Soft edges and irregular fibre hide the small asymmetries a sharp photo makes obvious, which is why felted portraits tend to read as affectionate rather than accurate. The style is doing something for you, not just to you.
Source photos that convert well
Directional light is the single biggest factor — a window to one side gives the wool somewhere to cast shadow, and that shadow is what sells the texture. Avoid heavy backlighting and phone portrait modes with aggressive background blur; the blur has no fibre to convert and often comes out as a smear behind an otherwise good portrait.