Wire mesh whose contour is your head profile at 1:1 scale.
Just (1) take a side view head photo,
(2) limit the extension of the profile and
(3) indicate a reference for the scale. The only limit is the max. size available for the chosen material.
Next, the three steps in detail:
1) Avoid low resolution and bad focused images. It's better to make the photo with the zoom/tele, filling all the frame with the head. No glasses (they won't be modelled and hide part of the nose) and lips closed (teeth aren't very artistic).
2) Crop the image to know the limits you want for the profile. They should be a point in the forehead and other in the chin/lower jaw. Or, instead of cropping, you can paint over the image to mark those points. Also you must indicate in the form the minimum and/or the maximum diameter of the object. The only limit is the max. size available for the materials: Strong&Flexible (23x18x31cm). So I'll keep you informed about the necessary changes and I'll ask for your approval.
3) To know the real dimension of your profile there are many methods. You can put a ruler over your sideburn/ear when making the photo. You can also use another object as you indicate its dimensions.