That's got a strong 1970s aesthetic to me, used to see things made with large applique in the sewing magazines of the time. I would think a simple rounded rectangle of the single image for each place-mat. The base color with a fused on frame of the blue (just zigzag, period would probably be that horrible nylon thread we had back then... I'd match the blue). Same with the overlay of the frame pieces. I think it would be cool to have place-mats with just the one side frame, you could put them all the same way or rotate them like the design there.
You are clever and can probably do some super cool stuff adding interest with your quilting. I'd probably wimp out and do some sort of all-over diagonal grid with a slight serpentine stitch -- but that inner frame part just has so many opportunities, along with the soft swirls.
For a runner, you could reduce the idea down to maybe a 6" block, 10" would be good. Part of that 70s thing was making blocks huge to be modern as opposed to tiny little fussy 30s triangles.