Fit a 1.3, it's the cheapest way.
The only other way is major engine work and even then you won't get much more power
Or buy a 1.3 micra
Cold air feed is pointless, as the coolant runs round the inlet manifold, so it's one step forward, one step back. Straight through exhaust is meh, but you'll loose out on torque, which these engines don't exactly have lots of, so try keeping one of the cats, or something.
There's no point trying with a 1 litre, unless you're willing to spend big money (more then the car is worth in most cases) so
i bypassed the coolant running through the TB with a spare pipe to keep the air cool, as the wax idle plunger was seized anyway and the front IAV works fine.
a further step maybe to fit an insulating inlet manifold gasket cos the engine blocks heating the inlet manifold hence the inlet air too.