Burchard of Worms wrote a penitential, a laundry list of questions for a priest to ask people in confession. One of the questions that could be asked of women was if they had made a strap-on and used it alone or with another woman.
I totally kid you not. It's pretty explicit about what is being made and how it's used.
It doesn't specify materials. Given that it would be constructed clandestinely (one assumes), I'd assume a stuffed leather rather than wood. This is an era before sandpaper, too, so just... no. I swear I remember reading about bread dildos somewhere, but again, ow. Maybe with an egg glaze? Fabric would get nasty quickly (and wool - ow; linen might be all right), but you might have a chance of keeping leather somewhat clean. And no ow.
I imagine I'd put it in a box with a sign "You must be 18 years of age to judge this entry."