Alan, thats why I'd start with exhaust first mate[]. Or, even changing your standard panel filter with a K&N or Green-Cotton filter is a good start on the breathing side of things IMHO.
go-back box, with deresonated centre section, cat-pipe and panel filter to start with IMHO. All done without a £500 remap.
If you decide to go for the full monty with decat, induction kit, Front mount intercooler etc later then you can get it remapped then.
Gus