external canister will indeed give you more room.
someone else will need to help you with the gllns side of things,
i use Fluval and find them nice and quiet,i have also used Eheim(that was internal)
but very good non the less.
all the media from your old filter can be put into a basket in the .....let's say Fluval,
and away you go.
you could put a thread in the equipment section and ask if anyone could help
you fix yours,or just get the new filter.
sorry i can't help much more than that i think.