If it’s been re-mapped you’ve arrived at the zenith of cost effective improvements..
Sports cat exhaust £1,000 5-20 BHP
Bigger turbo £2,000 20-35 BHP
Larger FMIC £500 10-20 BHP
Airbox ££ no change
After that it gets very expensive and potentially destructive…buy a 35i if you need more straight line speed..