You say an 'engine conversion is too extreme for me' in one breath and they say you are considering fitting a turbo in the next.
WTF ?
You are at cross-purposes.
So - first off - work out your budget. What you want to do depends on money.
There is heaps of info on 3S-GTE installs in place of 3S-GE and 5S-FE engines, spend a few hours on Google.
Not that you are likely to take my advice but one of the best upgrades for that car, shy of a 3S-GTE conversion is the Gen 2 123Kw engine from the SW20 MR2. You will not have to engineer the car, upgrade the brakes or have any insurance premium problems.