" i just dont think i have the know how or experience to build a sump yet"
NONSENSE!!! Experience is simply trial and error. A sump is about as simple as it gets. Its easier to maintain, cheaper to build and is, in my humble opinion, a better filter for larger systems.
However, a 55g isn't a huge tank. Its big, but there are good canister filters out there that would be more than adequate even for goldfish, which, by the way, aren't any more "dirty" than any other fish. Yes they have a simple digestive system so it seems they are more messy, but in reality, the fish will only create as much mess as they are fed. Over feed any fish and you will have water quality issues and an apparent need for massive filtration.
I have had a 55g with two Emperor 400s and that tank was sparkling even with an Oscar and a pleco. Thats the key though, it was ONLY an Oscar and A pleco. I had an Eheim 2026 proII on a 50g with 30-40 Africans. Water was crystal clear, no ammonia or nit.
I think if you are in the market for added filtration, get what you are comfortable spending on. As canister filters go, you wont go wrong with Eheim, but Eheim isnt the only game in town. The 2215 will give you about 3x turnover, the 2217 about 5x. Turnover is important, but if you are concerned about water clarity and media capacity, bigger is always better. I think a 2215 in addition to a HOB would be good. A Eheim 2217 by itself would be just about perfect provided you dont go crazy stocking the 55g
Good luck!