You may work with fabrics or or clays or items that are not quite flatbacked - if so, these could prove useful.  They have a slightly concave seat, in the shape of a shallow bowl, so you can easily cover the base with glue and then attach your makes.  We are seeing lots of fabric brooches at the moment and these will be perfect. They also have holes in case you prefer to sew on your toppings.

Available in golden finish, sold in packs of 10 pieces.