The Historic District

Mor-flexx. You can get in on Amazon. Paintable if need be but otherwise exactly what you need.

My 2 cents on making drywall mud or plaster skim coats stick to painted surfaces or base coats: bonding agent. The easiest is the kind you paint on the surface, I use Plaster Weld. Its basically glue. The big boxes don't carry it, so you might have to check a building supply yard. If you have a smal...