I usually use 9mm MDF and cover with Laminex as shown. The second template was made from a Laminex covered kitchen door recovered from a roadside skip together with many more. Off-cuts of Laminex can usually be obtained FREE from the skips behind Kitchen/bathroom workshops, with permission of course!
Even with my much used templates the inside edge of the templates has never given me any problems, but iron on edging strip can be used.
Nothing but heaven itself is better than a friend who is really a friend. - Plautus