12lbs is nothing. xD Bigger than our female cats, but our male is 18-20lbs, and the cat I catsit for has got to be at least 20, probably 22lbs. But our 18lb male is a Maine Coon, and the cat I cat sit for is a Norwegian Forest Cat Maine Coon mix. *phew!*
But that pic of your kitty is cute though! I've always wanted an orange and white cat.
My boy's a maine coon mix and about 20 lbs. Only a little of that is fat. He seems fine with our scratching post though. It's pretty big with a nice stable base. He actually fits in the hole pretty well, too. XD [link] Though I'll be honest and say I have no idea how he managed to actually get in there.
You could always try rubbing some catnip into it, use the scent to draw him to it. I've done that with similar things with my cat, and it seems to work pretty well.
Of course, it could also be a texture thing. Maybe he'd like a cardboard one better? (They also make the kind that are ramp-shaped [link] and maybe a little harder to knock over while he's scratching. They're also good because they have lots of holes on the surface you can sprinkle catnip into, so they're good for using that trick as well) You could also try making your own hanging scratching post with a piece of wood, find somewhere you can buy cheap carpet or fabric scraps and just nail/staple/glue them on. Your cat might like that more than the rope-wrapped scratching boards. (But I don't know how accessible those kinds of materials are for you...)