upgrades

Im ready for some more power but dont want to spend massive amounts. Unsure on what the next best step is , i am currently running the following: > Full Rossier exhaust >13 tooth front sprocket >Cherry Bomb >Uni Air Filter

i live in the UK so its pretty much always wet ! any recommendations on power based upgrades , currently running uni foam air filter, stock air box, cherry bomb, and have full rossier on its way .