Your best bet is to get some acid free foam core cut into circles. Don't use the sticky board, that's only good for catching critters and bugs. I would try thinner batting and layer it, using a few dress pins in the sides of the foamcore to test the poofiness to see how you like it. Once you get the right thickness, lace the xstitch around the foam/batting package with a cotton crochet thread to pull the art tight. Even though it's a circle, you want to treat it like a square while stretching (like there is a horizonal and a verticle). Once it's laced (don't sew it to the foamcore, just to itself) then you can adjust it until it is centered to your liking.
(I am a picture framer, been doing this for 20 years, this is my mom's account
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