There are many posts about this subject somewhere in the archives here I am sure... its an age old quandary.
Unfortunately there is little you can do, any kind of small floating plant, the likes of water lettuce, Salvinia
etc will just either get swirled around constantly or get pushed up into one corner of the tank and pile up on top of one another (this used to happen to me all the time).
having HOB filters it's probably impossible to alter the cascade of water flowing back into the tank which is causing the turbulence. If your return comes back to the tank via a spray bar or return pipe/nozzle of some description then these things could be angled so as to not agitate the surface of the water too much.
Then there is the question of to agitate the surface or not? I asked this question of the knowledgeable folk on here ages ago as every fibre of my being was telling me it was a necessity to allow gas exchange etc, but there are different schools of thought on this subject and apparently in a heavily planted tank too much water agitation can be detrimental to available CO2 for the plants (there are many other factors involved here, most of which I don't understand) Anyway, when I had floaters I used to alternate between surface agitation and messy, swirling floaters and no agitation and lovely still full coverage with my floating plants. I didn't like having no surface movement though, just didn't feel right!
Anyway, there is a floating plant you could try called Water Sprite
) if this plant does well it grows quite large, you get good coverage and may not spin and tumble as much as the smaller plants. or you could try a baffle of some description to cut down the flow of water coming from the filters. other than that theres not much else you can do.
As a side note, I used to be mad keen on floating plants but they just ended up being a pain and eventually all died off so now I don't bother with them. I just let my stem plants over grow and break off and float, this gives my fish a bit of surface coverage. I probably wouldn't go back to floating plants now, although there are guys that swear by them.
Hope this helps