I have done many of the same things. I have used construction paper cut to size, poster board, felt, plywood painted etc. I usually did put them in a frame with or without glass and not glueing but then the back of the frame would not fit back on. I have decided I like it without the glass whcih helps with the fit of the back. Portraits don'e seem to sell well around here so I don't do them much any more. The issue I had with felt is little particles stick to it easily and dust or airborn things so don't use that anymore. I have had better luck selling with use of the bass wood rounds with bark on and the portrait centered. works good with animals but people are fine also. I do glue a 1/8 or 1/16 in backer on it to hide the back. Just some of my thoughts. Like most things just comes down to personal preference and what customers or friends like.