Sadly your talking about the very expensive PPC/B-vision/c-vision route and since these cards are no longer made its a an even more expenxsive EBAY excursion.
While the the last two sales of B-vision have been £58 [incl postage] and £47 [inc p&p] which to some may not sound a lot
The PPC basic card an 040 /160 [ the same as Effy just parted with] sold for £267 , now thats a real kick in the teeth
At present their is an 060/PPC rated 210hz but thats standing at euro 323 with over a day left no doubt it will fetch considerably more
Since Effy's offer i have been watching prices and allthough I have a ppc have had to check this info for innsurrance purposes [ seperate thread ]
Fitting any improved graphics into an A1200 case is not a cheap or easy solution to your question as you can see from various threads on the matter.
Its only the genuine big box amiga's that can carry the improved graphics you ask about and still give you basic AGA to a single monitor.
The choice is yours
good luck