Floaters are a great addition to any tank and can definitely help soak up extra nutrients. Red root, frogbit, dwarf water lettuce and floating ferns are all great. Some people also chuck in floating hornwort if you like the look of that.
I'd suggest steering clear of duckweed or salvinia minima unless you like really aggressive, fast growing floaters that are impossible to get rid of. The latter is also invasive in a lot of places, so you have to make sure you are destroying the excess well.
You can keep floaters in place and allow light into the tank by using a piece of airline, made into a hoop with a coupler and just floating it where you don't want the plants to be.