It's not possible to have a decent looking Workbench screen even using a flicker fixer - scan doubler.
You need a very expensive tower case (can't find a new one), a very expensive PCI busboard (I think Elbox still makes them), a hard to find old PCI graphics card and a fast processor (can be found only second hand for lots of money) for this.
Or you need a BlizzardPPC (very very expensive. You can even buy a car instead of this card!

) and a BVisionPPC (very expensive and rare) preferably with a tower for the heat they generate.
Unfortunately the only native graphics card produced for the A1200 is the BVision and they are very hard to find. For example I have a partially working BlizzardPPC (well. Actually it doesn't work at the moment

) but can not find a BVision since they seem to be selling immediately once one become available for buying.
I wish there was some kind of cheap and old graphics chip we could plug on the A1200 mainboard like Indivision and it gave us high color RTG screens.