The Mediator 1200 SX (6 PCI slots), LT 4(4 slots) and LT (2 slots) don't need a ZIV busboard, they just plug onto the trapdoor expansion connector on the A1200 mobo. But you'll have to put the A1200 in a tower case. You'll also need some more RAM (4MB or more) and (preferable but not essential) an 030 or better accelerator.
Try to get a Blizzard 1230 Mk IV, or a Blizzard 1260 if you have plenty money, or even a Blizzard PPC if you're rich. But then you're getting into spending several hundreds of pounds on a machine that's way past it's best-by date.
