i recently got a TOM microfilter with a spraybar for my 5gal breeder off of amazon for like 14$. its quiet as ****, spraybar works good and plenty of power for 5 gal. its small internal with sponge and a little carbon.
I think I'll stick with the powerhead and sponge idea simply for size reasons, just got to research powerheads now to find a small one that is available in the uk! Thanks for your help guys!