An upgraded turbo will still be fine ran by a standard ecu provided you don't just think you cans wind the boost up, by far the easiest and most cost effective upgrade would be a t28bb turbo from some s15's. Cheap, ball bearing and slightly larger then the standard t25g.. I've seen these make 200rwkw+. Then the next 2 shoota has already covered, although it would be a waste to run them with the standard ecu and not extract the power they can deliver.

For a couple of examples, I have 2 mates using 2871R's,Both running 040 pumps and 700cc injectors one is just basic bolt ons and a nistune, 15psi it makes 220rwkw
Other one has a Haltech ps1000 ecu and poncams, 20psi it makes 280rwkw.
Now that would be fun in a 1200!!